# Marshall AVT50 Mods



## Peter

I came up with some great modifications for my AVT50 amp:
1. The obvious mod: add a second speaker jack.
2. Installed a clean channel midrange control.
3. Increased preamp tube gain by around 25% (switched).
4. Installed a 6 position mid shift switch on the Overdrive channel with the stock midrange frequency, and 5 others [a great mod in any amp].
5. I reinforced some key components in the amp with higher wattage and voltage components (cheap insurance).

The *fatter tones *from the mid shift switch along with the *extra tube drive *really really brought the amp to life. The amp sounds 100% way better, and I didn't even drive the tube nearly as hot as in other tube amps. The clean channel tube sound really rocks on full gain, and rolls off at lower gains. Very impressive improvements. I am also working on an optoelectronically controlled footswitch for Lead Boost and Scoop. Anybody out there interested in Kits? I am interested in producing them.

PETER THE TONE DOCTOR


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## Peter

I can't understand why nobody has responded to this post - I took a really good amp, and significantly improved it. Another technician/guitar player I know who only plays tube amps made this comment to me when I was demonstrating the clean channel to him yesterday : "You would be hard pressed to tell it from a tube amp now". Wake up people. These mods rock.

PETER THE TONE DOCTOR


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## Peter

UPDATE: I made my tube boost mod footswitchable! Works great, with silent switching, and LED! Go from stock sound to tube boost. Works great!

PETER THE TONE DOCTOR


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## wolf1419

Peter said:


> I can't understand why nobody has responded to this post - I took a really good amp, and significantly improved it. Another technician/guitar player I know who only plays tube amps made this comment to me when I was demonstrating the clean channel to him yesterday : "You would be hard pressed to tell it from a tube amp now". Wake up people. These mods rock.
> 
> PETER THE TONE DOCTOR



I found this to be exciting!! Great work!! It's just that most of us "regular guys" without electronics knowledge wouldn't know how, or would be afraid to attempt these mods, so that's probably why everyone's so quiet. We don't understand how to accomplish major feats like that. 
I have a Marshall Mode Four MF350 that is similar technology(tube/hybrid) and I have a quick "pop/crack/thump"(spike) sound on powerup(no standby like tube amps), and I can't even figure that out. Marshall support hasn't been able to help. I have 2 of these and they both do it, but it's sometimes softer, sometimes harder sounding. Other than this the amps are excellent sounding-many tones can be tweaked from this beast. Do you have any clues on the spike, or is it just a solid state thing??


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## Peter

*Re: Marshall AVT50 Mods and POP sound*

Thanks so very much for your response. I am looking into the pop thing. I believe a friend of mine (also a tech) may have the answer to this one. As for the mods, I am working on a kit that you can take to your tech, or if you are a hobbyist with some basic knowledge of soldering and electronics components, you can install yourself. I plan to supply detailed instructions, and provide as much support as I can. Cheers!

PETER THE TONE DOCTOR


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## Peter

wolf1419 said:


> I have a Marshall Mode Four MF350 that is similar technology(tube/hybrid) and I have a quick "pop/crack/thump"(spike) sound on powerup(no standby like tube amps), and I can't even figure that out. Marshall support hasn't been able to help. I have 2 of these and they both do it, but it's sometimes softer, sometimes harder sounding. Other than this the amps are excellent sounding-many tones can be tweaked from this beast. Do you have any clues on the spike, or is it just a solid state thing??



Hey wolf, apparently, the popping is an inherent problem in solid-state amps. The problem is that when you first start the amps, capacitors in the circuitry are in a discharged state, and they pop when power is applied to them. I tried two solid-state Yorkville Sound amps I own, and they both pop, albeit not too loudly, until they have been on for maybe 20 or 30 seconds, then you can turn them on, and since the caps are then fully charged, they don't pop. My Marshall AVT50 amp, on the other hand, has a power module (the main amplifier chip, which is connected directly to the speaker), that has a built-in standy feature, which delays output for a few seconds when it is powered up, so that the amp's capacitors don't pop audibly (great feature). Tube amps don't have this problem, because the power tubes don't amplify until they are heated up, during which time you are on standby anyways, so you don't ever hear any pop. Most amps with a solid state power amp come on right away, and therefore pop. Nothing much you can do about it. Do you like my explanation?

PETER THE TONE DOCTOR


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## wolf1419

Peter said:


> Hey wolf, apparently, the popping is an inherent problem in solid-state amps. The problem is that when you first start the amps, capacitors in the circuitry are in a discharged state, and they pop when power is applied to them. I tried two solid-state Yorkville Sound amps I own, and they both pop, albeit not too loudly, until they have been on for maybe 20 or 30 seconds, then you can turn them on, and since the caps are then fully charged, they don't pop. My Marshall AVT50 amp, on the other hand, has a power module (the main amplifier chip, which is connected directly to the speaker), that has a built-in standy feature, which delays output for a few seconds when it is powered up, so that the amp's capacitors don't pop audibly (great feature). Tube amps don't have this problem, because the power tubes don't amplify until they are heated up, during which time you are on standby anyways, so you don't ever hear any pop. Most amps with a solid state power amp come on right away, and therefore pop. Nothing much you can do about it. Do you like my explanation?
> 
> PETER THE TONE DOCTOR



Peter, thank you sooo much. It makes sense and I was wondering why both amps did it to varying degrees, a little different each time. These are also 350 watt amps, tube preamps, so maybe just a little more brutal with the startup than some smaller amps. That's a better answer than I got from Marshall. I'm just wondering why no one else has mentioned it, since it seems a little odd to me. Thanks again, and if you hear anything else about this please don't hesitate to add to it.


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## Peter

wolf1419 said:


> Peter, thank you sooo much. It makes sense and I was wondering why both amps did it to varying degrees, a little different each time. These are also 350 watt amps, tube preamps, so maybe just a little more brutal with the startup than some smaller amps. That's a better answer than I got from Marshall. I'm just wondering why no one else has mentioned it, since it seems a little odd to me. Thanks again, and if you hear anything else about this please don't hesitate to add to it.



Glad I could help.


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## perkristian876

How about some pictures? looks like a great mod. Easy to perform?


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## Peter

Seems easy to me. A certain level of skill is required anytime you modify an amp that has circuit boards though. I am working on producing a kit, with detailed instructions, and all the necessary parts and wiring. Cost will be at issue, as I put $60 worth of parts into mine, but the kits will be simpler of necessity. I truly feel I made a $500 amp into a $1000 amp though; it has found powerful identity and flexibility through the footswitched boost on both channels, and the mid-shift on the dirty channel. Very usable, with 4 distinct voices. I may mod a few of these amps, and sell them on ebay to get the ball rolling... These amps are going to become very popular, I believe. Currently, I need to start producing circuit boards, because I don't think project boards will do much for my reputation, even if they are only 1.5"x1.5". I will keep you posted...


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## UnChained!

Hello Peter, I've been watching this thread for a couple months now and finally decided to join the forum. I have an AVT50H with both AVT412A & B cabs. I truely love the flexibility as it supports the varying types of music I play. However, I've always thought that there could be just a little more... Then I saw this thread! The only real changes I've made were to the cabs. I removed all of the stock Celestions and replaced the with 8ohm Emi Legend V12's and Legend GB12's in an X pattern. Seemed to remove what I always thought of as "harshness" especially in the OD channel.

Your mods are very interesting to me. Please keep us posted. I have limited experience fiddling with electronics of this nature, but would be willing to try if simple enough.

Thanks for the info so far. Looking forward to more.

Chip


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## Peter

Sorry everybody, I am in and out of town all summer. I take my amp with me, and it has been great! It really blows away the stock amp by a mile (and I loved it even before I made the changes). I plan to add mid-shift to the clean channel next (already have parts), and add a 120V AC power outlet for accessories. I am also considering adding a master volume (attenuator), so that you can adjust both channels for balance between clean and dirty (turned up to the max) with the existing controls, then adjust the overall volume of both channels without messing up the balance between the channels. When I finally work everything out, you will all hear about it. I hope many people will be interested. Many of these mods will work in other amps. Here are some photos, as someone on this thread requested. The black knob above the CH2 mid control is the CH2 mid shift (I plan to replace the black knob with a Marshall knob, as soon as I have obtained one). The toggle switch above the channel switch on the front panel does the same job as the footswitch I added, and will not be a part of the final kit, as it is redundant, and makes everything harder to install. The knob on the back is the clean channel mid. I plan to locate the clean channel mid-shift knob next to the clean channel mid control on my amp. All of the controls can be mounted on the back panel, for those of you that prefer not to drill holes in the front (I prefer front panel access, and don't care about drilling holes in the front panel). Please offer me your suggestions and comments if you have any. Have your say as to how it should be done. Cheers, all!

PETER THE TONE DOCTOR


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## coldsteal2

COOL, this is the first time i have seen this thread


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## Peter

coldsteal2 said:


> COOL, this is the first time i have seen this thread



Hey, Cliff! I'm listening to some of your originals... Wish we could jam! I'm all the way up in Toronto, Canada, lol... Keep rocking!


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## DragonSarc

question what does the preamp tube do? i kinda figured that (like the jcm 900 has 3 preamp tube) is it 1 for clean which is V1 and 2 is for the OD on V2 and the 3rd is the phase inverter which balance the pre amps or all the preamp tube works on both clean and OD?


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## amplifier

DragonSarc said:


> question what does the preamp tube do? i kinda figured that (like the jcm 900 has 3 preamp tube) is it 1 for clean which is V1 and 2 is for the OD on V2 and the 3rd is the phase inverter which balance the pre amps or all the preamp tube works on both clean and OD?



All the tubes are working at the same time regardless of what channel you're on. With your 900 the V1 and V2 would mostly affect your gain and tone. The phase inverter drives the current into your poweramp section. When you order tubes for your phase inverter make sure you order one with balanced triodes. The other 2 don't need to be balanced.


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## DragonSarc

amplifier said:


> All the tubes are working at the same time regardless of what channel you're on. With your 900 the V1 and V2 would mostly affect your gain and tone. The phase inverter drives the current into your poweramp section. When you order tubes for your phase inverter make sure you order one with balanced triodes. The other 2 don't need to be balanced.



thanks for the reply amp - so basicaly the more preamp you have the more gain you get? like the DSL/TSL amp has 4 preamp tube and has more gain than the 900 is that right?


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## amplifier

DragonSarc said:


> thanks for the reply amp - so basicaly the more preamp you have the more gain you get? like the DSL/TSL amp has 4 preamp tube and has more gain than the 900 is that right?



Woops I can't believe I almost forgot the effects loop, that's got it's own tube which your 900 has. It's probably V1=gain, V2= effects loop, V3= phase inverter. Sometimes the last preamp tube controls the effects/loop, and sometimes the phase inverter, it depends on the model but that should give you a good idea of how it works. I'm not exactly sure how it's set up on the 900's but Coldsteal will probably know. 

If the extra tubes are part of the gain stage than yes more tubes = more gain but more gain doesn't equal better tone!


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## CapnCrunch

Peter,
I have 3 AVT50H heads (VS2000). I love em! I was thinking about replacing the pre-amp tube with a Groove Tube (GT has a nice Mullard 12ax7 re-issue - or else I may go wth their GT-ECC83) - There is quite a waiting list for the Mullard re-issues!

Do you think I'll notice a difference in performance if I do this? Or should I hang on to my cash?

I love the fact that YOU have taken an interest in this model. My third head is "blown". (I run 2 half-stacks in stereo - the third is a backup head). I turned it on with the volume way up.........now..it turns on, but I get a faint, fuzzy output signal through my cabinet (I tested with another cab to make sure it wasn't the speakers).

I'd like to play Frankenstein with it now that there are mods (thanks to you!) but I'm like most folks and can just swap pre-amp tubes at best.

Thanks for your time,
CapnCrunch


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## Arcarix

Hi Peter,
Thank you! Someone has finally seen the potential in this amp! This is something I have been waiting for. These are the exact mods I want! 
I have the exact same amp and am interested in your kit. These are the exact same mod's I would have made on my own. I am very experienced in working on amps ( Twin Reverb especially)and would have no probs doing this. Have you considered just selling wiring diagrams? Personally, I would prefer a kit that includes all the parts as sourcing the parts is sometime an insurmountable prob.


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## Peter

*Quite right, Amplifier*: the way the tube works in the AVT50 is on both channels. The pre-amp feeds into the tube. On channel 1, the tube is fed a clean signal, which overdrives the tube's input when the gain is up. With my mods, channel 1 gets some serious tube crunch on full gain. Channel 2 is like having a built-in distortion pedal in the preamp before the tube. 

*CapNCrunch*, finding the right tube for you is pure trial and error. I tried over 15 tubes, and most sounded average, and some sounded flat. I am lucky for my old made-in-holland Rogers tube, which crunches, but still sounds sweet. I found I do like the Sovtek 12ax7wb tube, which is not expensive. 

*Thanks for your input, Arcarix*. You are right about the parts; I get some of them from surplus. A complete kit, as well as a web-site are on the horizon. Thanks very much for your interest.
Cheers!


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## skyryder1212

I just picked up one of these used, and am interested in the mod kit. Any idea of pricing and availability. Any youtube or sound files?

Thanks.


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## Peter

skyryder1212 said:


> I just picked up one of these used, and am interested in the mod kit. Any idea of pricing and availability. Any youtube or sound files?
> 
> Thanks.



I am working on a limited run of the circuit boards. I just bought the laser printer, special print paper, etching chemicals, and a copper board needed for the project. I am drawing up a circuit board right now (I did mine using a project board). I will put up an update ASAP. Thanks for your interest.

PETER


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## AA703

I am interested in the mod kit also.


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## Andypandapedal

This is awesome stuff!
My AVT50 just got put on the bench, I may wait for the kit now!
Very COOL!


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## skyryder1212

There is a Service Bulletin out on the AVT150's that recommends installing a couple of Xener diodes on the input......does any one know if that also applies to the 50's? I do get a lot of buzz on the distortion channel...


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## Peter

skyryder1212 said:


> There is a Service Bulletin out on the AVT150's that recommends installing a couple of Xener diodes on the input......does any one know if that also applies to the 50's? I do get a lot of buzz on the distortion channel...



Are those diodes supposed to go to the +- 15v supply? If so, the AVT50 already has them. They just limit the signal going into the first op-amp so the signal doesn't exceed the op-amp's maximum input rating.

PETER


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## Peter

Re: Mod Kits

I have never made circuit boards before. I am waiting for a friend to supply me with some pyrex containers to handle the acid for etching the boards. I already have the chemicals, the copper boards (I got some really good old ones with lots of copper on them from surplus), special transfer paper, laser printer, and the circuit board designs. Once I have a run of circuit boards successfully made, I will dish out for the more expensive parts, and put out the kits. Initially, for the first run, I will customize the kits for what each person wants, and I will ask for some feedback, to help me standardize the kits. 

I have also been building a web site where I will be showcasing my mods. There will be a new forum on my site, to talk about, and help develop mods. You will all be invited to join me there. Thanks for your patience and encouragement, all. 

If anyone want to email me directly, my email address is octopussy@ca.inter.net

PETER


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## SlickTop

*Need Help With JVM410H*

Hello all, i'm new here. Just got a new JVM410h w/ 1936 2x12 Cab.

I'm confused as to which speaker output/input jack to use. Below are the options i have.

Amp Head Outputs: 1x4 ohms* 2x8 ohms*1x8 ohms*2x16 ohms*1x16 ohms.

Cab Inputs: Right input 16 ohms___Left input 16 ohms or Mono input 8 ohms.


Mark me confused, i'm new to the Marshall lifestyle....Please Help!


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## Peter

*Re: Need Help With JVM410H*



SlickTop said:


> Hello all, i'm new here. Just got a new JVM410h w/ 1936 2x12 Cab.
> 
> I'm confused as to which speaker output/input jack to use. Below are the options i have.
> 
> Amp Head Outputs: 1x4 ohms* 2x8 ohms*1x8 ohms*2x16 ohms*1x16 ohms.
> 
> Cab Inputs: Right input 16 ohms___Left input 16 ohms or Mono input 8 ohms.
> 
> 
> Mark me confused, i'm new to the Marshall lifestyle....Please Help!



Amp Head Outputs: 1x8 ohms
Cab Inputs: Mono input 8 ohms


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## coldsteal2

yea it would be great to have a mid EQ for the
clean channel

dont forget for the combos puting in a V-30 really
improves the tone


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## Arcarix

CS2-
Could you post some sound clips of yours with the V30's ?
THX


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## Peter

Funny thing, I tried a celestion vintage 30 (chinese) in my avt50 (from avatar sound). I didn't like it - it was way too efficient, mid-rangy, and directional, so I couldn't turn up the amp without blowing out my ears, and standing in front of it could kill you. I found the amp didn't sound right turned down so low either; you need to turn it up somewhat to get a good sound. Opening up the back 1/3 helped, but it was still way too honky. I replaced it with a 4 ohm celestion g12m70. If you play rock and blues, this is the speaker for you. Much much much better, IMHO. The only other thing I may eventually try is putting an aluminum dome on the g12m70. Cheers!

Peter


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## john_lisi

So Peter,are the stock speakers designed to have a scoopy mid? If so what you are telling is is that a new speaker can drastically improve the mids.Also is there a way to change the treble value because I have it on 0-2 and it's still too bright ( with a les paul to boot) with a strat it would be unbearable.I like the amp but with a few changes it could sound stellar.....


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## brecab

Hi Peter, My name is Fred and I realize this is an old thread from march, but I am really interested in your mods for the avt50. I have one and I love it, but it's just not quite as versitile as it could be. Your mods would definitly address the issues I have with the amp. I'm not a tech as far as electronics goes but I do all my own guitar electronics so I can usually figure out schematics and am real adept at what it takes to do whatever work on the chassis that needs to be done. You may have a kit already, I don't know but I would definitly be intersted in one, even if it is just the directions and schematics and a parts list if your not set up for parts yet.


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## Peter

john_lisi said:


> So Peter,are the stock speakers designed to have a scoopy mid? If so what you are telling is is that a new speaker can drastically improve the mids.Also is there a way to change the treble value because I have it on 0-2 and it's still too bright ( with a les paul to boot) with a strat it would be unbearable.I like the amp but with a few changes it could sound stellar.....



I liked the sound of the stock speaker, but it couldn't handle the power. A half hour playing purple haze and hey joe on 10, and it popped; go figure. Smelled like a barbeque. As for treble, that's the reason guitars have tone controls. Mid shift also helps dramatically. Cheers!

PETER

AVT50 mods link:
http://www.marshallforum.com/workbench/859-marshall-avt50-mods.html


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## Peter

reply to Adam's email: 

Dear Adam, I will experiment with shipping overseas. I will not be sure of the cost until I have produced my first batch, shipping will be whatever the cost is (not in my control), plus perhaps a modest handling fee (yet to be determined). The circuit boards will come pre-soldered. Since the number of features will affect cost, the number of features will be based on what people are willing to spend. Initially, I will custom add features by order to help determine the final kit form/cost. These features will definitely be a part of the kit: 

1. Clean channel mid range control
2. 25% pre amp tube gain boost footswitchable for channels 1 & 2 with silent switching & pedal LED (you will have to modify your pedal, and the pedal jack will have to be replaced on the back of the amp with a special one, along with a new secondary jack, I will provide the parts, the 4 conductor wire, and detailed instructions)
3. Mid frequency shift control channel 2 (6 positions, including original unmodified channel 2 amp tone)
4. A few higher wattage and voltage components


I have not tried adding the mid-shift to the clean channel yet, but I have the parts, I just haven't had the time. I haven't seen if the master volume is feasible yet. I don't have sound clips yet either, but the mid-shift on CH2 is dramatic and a key feature. As for tube boost the amp sounds stock, but when you add boost, the tube adds even order harmonics, and sounds like any breaking up tube amp, depending on gain setting (I scoped the results, and they clearly show I am bringing the tube into natural tube saturation/compression). 

Whew! I hope this answers your questions! I am leaving on vacation now for about 20 days. I am posting this on the site. Cheers!

Peter


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## Arcarix

Hi Peter,
Just my prefs on your proposed mods.....

1. Definitely want that
2. Definitely want that
3. I rarely use chan. 2, so not a biggie for me. 
4. Never a bad idea, I can deal with that

Could you include a diagram for the ext. spkr cab jack? Or maybe a photo? Anyone that can do these mods as proposed should be able to do that with just simple instructions.


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## dnz.mtn

hey Peter,

i'm planning to buy an avt-50. The first thing i'll do is adding a midrange control for the clean channel. i haven't gone thru all the posts, so i'm not sure if you already provided a diagram for the modification. i'd be happy if you could send me such a diagram...
thanks
deniz


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## Arcarix

Hi!
I tried changing spkrs from stock to Eminence Patriot 'Red white and Blue', which is an 8 ohm 120 watt spkr. Although it sounds good when some volume is applied (also use Boss effects in the effect loop - GE7 with mids up, slight compression w/CE3, and slight CS3 delay instead of reverb), I don't think the power/tone potential of the amp is being used to best advantage with this spkr.Any thoughts on this setup would be appreciated, as well as your thoughts on impedance matching (8 ohm spkr to 4 ohm amp). Thanks, still looking forward to getting your mods!
Arcarix


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## Pete240885

Miss matched impedance WILL kill your amp


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## Peter

Dear all, I am back. Progress report: I have successfully produced my first circuit boards, though not for the AVT50 yet (these will be next, I am currently modifying the design for the AVT50 board a bit more, and improving my procedures for making circuit boards). I have had to face some challenges. I am awaiting parts I ordered for the AVT50 mods. I have ordered enough parts for about 13 kits. Some of the parts I am searching for are a bit hard to find - I may have to alter my designs a bit if I can't locate them. I plan to have the kits out before the end of 2008. Thanks for everybody's interest.

Dear Arcarix: the extension speaker jack mod is the easiest part of the kits, when installing tube gain. Have no fear, instructions will come with the kits. As for the speaker, I am using a 4 ohm celestion g12m70, which, IMHO, matches up with the amp beautifully. As for speaker impedance, using a speaker rated at a higher impedance than the amps is harmless, but if you run an 8 ohm speaker in a 4 ohm amp, your power gets cut in half. if you run a 16 ohm speaker in a 4 ohm amp, your power gets cut in 4. 4 ohm speaker with 4 ohm amp=100% of your power. WARNING: NEVER USE A LOWER IMPEDANCE SPEAKER THAN THE AMPS IMPEDANCE RATING, AS THAT WILL CAUSE SEVERE DAMAGE TO THE AMP. 

PETER


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## Pete240885

Peter said:


> As for speaker impedance, using a speaker rated at a higher impedance than the amps is harmless, but if you run an 8 ohm speaker in a 4 ohm amp, your power gets cut in half. if you run a 16 ohm speaker in a 4 ohm amp, your power gets cut in 4. 4 ohm speaker with 4 ohm amp=100% of your power. WARNING: NEVER USE A LOWER IMPEDANCE SPEAKER THAN THE AMPS IMPEDANCE RATING, AS THAT WILL CAUSE SEVERE DAMAGE TO THE AMP.



I studied amplifier design in the seccond and third years of my degree, this does not agree what i've been taught.

If the power is not being fed to the speaker then it is being dissapated inside your amp, therefore an impedance missmatch, be it too high or too low, is bad.


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## PaoloJM

Pete240885 said:


> I studied amplifier design in the seccond and third years of my degree, this does not agree what i've been taught.
> 
> If the power is not being fed to the speaker then it is being dissapated inside your amp, therefore an impedance missmatch, be it too high or too low, is bad.



This seems to be a bit of a grey area. This is my understanfing:

Amp type and Class bias are effected slightly differently by load mismatch.

In a Class A biased amplifier mismatched load does not cause power dissapation problems. 
Power dissipation is maximum in Class A when the amp is idling. A change in load simply rotates the load line either way and does not cause additional power dissipation. With a signal applied a lower load (assuming it's not a large mismatch) will not cause any problems but may noticably affect the frequency resposne. A higher load may cause higher than expected signal voltage peaks which, if above the limits of the valve/transistor or OT (if present), could cause problems. Power delivered to the load will be reduced.

In Class AB a load mismatch is more serious. A lower load is never a good idea in Class AB as you will most likely cause excessive power dissipation in both the valves/transistors and OT (if present). It effectivley rotates the load line right above the max dissipation level. A higher load may also cause problems with excessive signal voltage peaks. 
However most good amps are desined with valves/transistors and OTs (if present) that are rated well above the max voltages expected and a higher load (again within reason) can usually be tolerated but will cause reduced power and changed frequency response.

In short, a higher load is ok but not ideal in both Class A and AB.
A lower load is ok with Class A but definitley not in Class AB and solid state amps are designed to drive multiple different loads ( 4, 8 or 16ohm) but will put out maximum power to a certain specified load.

This is based on my reading so far from sites like The Valve Wizrd, Electronic Circuit Theory text books, RCA manuals and a Designing Solid State Amplifiers pdf book that I downloaded.

However I may have interpereted some of this info incorrectly, does anyone have a definitive answer on this?


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## Pete240885

PaoloJM said:


> In short, a higher load is ok but not ideal in both Class A and AB.
> A lower load is ok with Class A but definitley not in Class AB and solid state amps are designed to drive multiple different loads ( 4, 8 or 16ohm) but will put out maximum power to a certain specified load.



There is a genereal rule of thumb that will change the way you look at this:

Solid State amplifiers will GENERALLY survive an open circuit (extreme high impedance) but not a short circuit (extreme low impedance)

Valve amplifiers will generally GENERALLY survive a short circuit , but not an open circuit.


Note the word generally, this indicates that this is not always the case, now considering that an impedance miss-match is simply a less extreme version of the above two scenarios, it should be fairly clear that an impedance miss-match (either higher or lower) is not good for your amp.


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## Peter

*Re: AVT50 Mods - addition of clean channel mid-shift*

*NEWSFLASH:* I added a 6 position rotary mid-shift switch to my clean channel yesterday. The amp produces a world of new tones now. Today, I had the house to myself, so I took out a Les Paul Deluxe [gibson mini humbucker pickups with alnico magnets, which make the guitar sound between a les paul and a fender strat] and rocked out. With tube boost off, and gain at 5, the amp sounds sweet and clean, for chording and rhythm. With tube boost kicked on, mid-shift set to stock setting, bass at 10, midrange at 5, treble at 8, gain on full, volume at 3/4, the amp really rips, but the highs could kill you. I rotated the mid- shift switch 4 clicks, moving the highs deep into the mid-range, fattening up the tone significantly, and making the sound less ear damaging as a bonus. It really hummed, with sweetly beating frequencies. Powerful sound, and singing leads. I couldn't stop playing. Pure tube sound heaven. A very satisfying mod. A huge improvement in this amp's clean channel flexibility, at any gain setting.


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## Colbebi

I have two questions for this group:
1. When switching channels (both with footswitch and on the front panel) of my AVT50, the volume spikes very high for a brief moment, then returns to normal. It is quite alarming and can wake the rest of the house when I play late at night. Does anyone have ideas what might be causing this and how I might fix it?
2. Can someone tell me how to bias or adjust the gain of the preamp tube?

Thank you!


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## Peter

Quote:
Originally Posted by Vince 
Hi Peter!
I am interested in your mods for the valvestate amps. I am getting ready to purchase one so of course I am looking around to see how to get the most out of them...

Thanks!
Vince 

Great! I have ordered key parts for 13 kits. Some parts, I am scrounging for. When I'm ready, whoever money-orders me first will get them (I am putting out a chunk of change to do this). These amps are capable of great tube sound. Mine is awesome. Thanks for your interest, Vince!

Peter


----------



## Peter

Quote:
Originally Posted by formercakid 
You seem to have a very high knowledge level of amp electronics and amp speaker selection. Can you give me a suggestion for a speaker to replace the stock speaker in the DSL-201(201 IS THE 20 WATT MODEL)? 

I do know amps, but nah, I only know a thing or two about speakers, especially, I know when it sounds good. The Vintage30 sounded bad in my avt50 (in my opinion), and the 4ohm celestion g12m70 works great with the amp. A friend of mine favours old JBL speakers with alnico magnets and aluminum domes, but good as they are, they may not be to all tastes; they sound INCREDIBLE distorted, but are not as sweet as some clean, though they handle massive power and are of very high quality. I am thinking about trying replacing the paper dust cap in the center of my g12m70 with an aluminium one - I bet it will make this amp sound deadlier. Cheers!

Peter


----------



## Voland

Hi everyone

I have an issue with my AVT50 - when I turn it off, I sometimes (80% of the time) get a loud pop from the speaker. 
As far as I know, the cause for this is the discharge of the capacitors, which still have some charge on them. Does anyone have an idea how to fix this problem?

Cheers


----------



## Peter

Voland said:


> Hi everyone
> 
> I have an issue with my AVT50 - when I turn it off, I sometimes (80% of the time) get a loud pop from the speaker.
> As far as I know, the cause for this is the discharge of the capacitors, which still have some charge on them. Does anyone have an idea how to fix this problem?
> 
> Cheers



Usually, solid state amps pop when you turn them on. Last time I had a problem with an amp popping when turning it off, one of the capacitors had a cold solder joint. Re-soldering the capacitor fixed the problem. 

Troubleshooting: [if you don't know how to do this safely, or if you don't have the skills to do it, go to a technician, even if the amp is un-plugged, capacitors can hold enough charge to hurt you, especially the main filter caps] - I would start by opening up the amp, turning it on, and poking around, using a stick (or other non-conductive probe). Push and tap on components to see if you can find one that causes noise/crackling (out the speaker). Try pulling out the tube, and seeing if you still get the pop - if you don't, you know it is in the circuit before the tube, if you do, it is after the tube. If that doesn't reveal the problem, try dis-charging the electro-lytic caps, and re-soldering them. It could be a non-polarized cap causing the problem as well. If that doesn't work, you may be looking for a bad cap or cold solder joint, I am guessing. Best of luck. Please let me know if this helps.

Peter


----------



## RMiller

Hello Peter,

I am vary interested in your Mod Kit, how much will it cost to order a kit and is this something anyone can do or will a tech have to do the mods? Please email me the info at 59elcamino@earthlink.net. Thanks


----------



## Arcarix

>Peter
You still around?


----------



## Voland

Peter said:


> I came up with some great modifications for my AVT50 amp:
> 1. The obvious mod: add a second speaker jack.
> 2. Installed a clean channel midrange control.
> 3. Increased preamp tube gain by around 25% (switched).
> 4. Installed a 6 position mid shift switch on the Overdrive channel with the stock midrange frequency, and 5 others [a great mod in any amp].
> 5. I reinforced some key components in the amp with higher wattage and voltage components (cheap insurance).
> 
> The *fatter tones *from the mid shift switch along with the *extra tube drive *really really brought the amp to life. The amp sounds 100% way better, and I didn't even drive the tube nearly as hot as in other tube amps. The clean channel tube sound really rocks on full gain, and rolls off at lower gains. Very impressive improvements. I am also working on an optoelectronically controlled footswitch for Lead Boost and Scoop. Anybody out there interested in Kits? I am interested in producing them.
> 
> PETER THE TONE DOCTOR



How did you manage to increase the gain by that much? - I've tried to increase my preamp gain by adding a 4.7 uF capacitor in parallel to the first cathode resistor(R29 on the official schematic), which kinda improved the distortion, but it's nowhere close the 25% you're talking about. I didn't actually measure anything though. Cheers, Ivan


----------



## Martdogplay

Hi Peter,

I am interested in purchasing your mods for my amp.Please email me with pricing and availibility. To rocket1101149969@sbcglobal.net


----------



## Martdogplay

Hi Peter,

I would like to add a selectable ohm switch for the output of the amp,like the old ones 4,8, and 16 ohms.Can you send me info and pictures on how to do that.

Thanks,
Marty


----------



## Fixr1984

I think I figured out the mid shift and made both channels have a footswitchable gain boost.
I have to play my amp a little bit more to see if the values I chose are worth keeping before I put everything back together.


----------



## Peter

*Re: Impedance Switch*



Martdogplay said:


> Hi Peter,
> 
> I would like to add a selectable ohm switch for the output of the amp,like the old ones 4,8, and 16 ohms.Can you send me info and pictures on how to do that.
> 
> Thanks,
> Marty



Sorry, Marty, the old amps had output transformers with coil taps for various impedances, these amps don't.


----------



## Peter

I designed all of my mods for the AVT50 combo, and would like to make sure they are compatible with the head. Would anyone out there be willing to send me some high-resolution digital photos of the inside of an AVT50H head? Many thanks.


----------



## Fixr1984

I have the head version. Are you looking for up close parts of the board? Certain parts of the inside? The whole thing? Let me know I can get you some pics. Maybe we could trade some mod info. I am currently doing mine but with a 4 position switch and was curious to what values you chose. Also what value you used for the gain boost. I definatly have boost but wasn't sure if I went to the full potential.

Jason


----------



## Fixr1984

I've been messing with Duncan tone stack calculator just to see what values would work best without messing too much with the bass and treble as well. Seems to me that in some cases a bass shift control might be useful. I have the room to add it as well as the components to make it work so I just might give it a try. Any other thoughts on that idea?


----------



## Peter

Hi, all, I have been away. Since returning, I managed to improve my AVT50 mods some more, and came up with some new mods for the future. I am making my kits compatible with upcoming mods as well. I'm currently shopping around for a second AVT50 to try out my kit before sending any out. Best wishes.

PETER


----------



## joelschaos

Hey is anyone gonna post instructions on how to perform these mods yourself? I am mostly interested in adding the mid eq control on the clean channel. Any info would be much appreciated...


----------



## Arcarix

Peter, I am definitely interested in buying your mods when you are ready to sell them.
I'm about to replace the current 8 ohm speaker i used to replace the stock speaker. 4 ohm 12" spkrs seem to be difficult to find, however I have found a source for Jensen C12-N spkrs.

I e-mailed the owner asking if it was a good fit for the AVT-50, and here is his reply (I'm not affiliated with these people, and havn't even bought the spkr yet so I don't know how they sound)...

"hi, i found the C12N-4 to be a perfect speaker for that amp.
dont be fooled by the cost... this is a really articulate musical instrument speaker.

here is the link... feel free to log in and use the shopping cart to calculate your exact cost to your door please:

Jensen C12N-4 - VintageSpeaker.Com

ps we only take PayPal or Money order, we are a distributor.

thanks in advance,

Joseph A. Scinta
President KEN-TON Electronics Inc.
187 Greenacres Rd.
Tonawanda, NY 14150 (716-837-9168)

PRODUCTION Facility:
KEN-TON ELECTRONICS INC
2256 Sheridan Drive
BUFFALO NY 14223 (716-875-5114)

VINTAGE SPEAKER LOGIN

Main Phone: 1-(716)-837-9168 Fax: 1-(716)-833-3319j"


----------



## Peter

Arcarix, I am interested in hearing your opinion on the Jensen you are buying, as compared to the stock speaker. Incidentally, I just had to troubleshoot my AVT50 - I thought my mods had possibly added a slight buzzing to the clean sound, but it turns out the speaker was the problem. I determined this by connecting the speaker to another amp, which resulted in the exact same buzzing. I suspect something is loose in the voice coil. I hope I can fix my 4 Ohm Celestion G12M-70, because it is really good in this amp. I hope to hear from you soon on the speaker topic. All the best.

Peter


----------



## Arcarix

Sure thing Peter. It'll probably be 2 weeks to buy & install the Jensen, then A/B the two for a week. I'm hoping for a kind of half Marshall/half fender tone to use with my strat. I'll keep in touch.


----------



## Arcarix

Hi! Jensen C12N-4 got here about 2 hrs ago, it's installed, and I'm hype'd! It sounds GOOD! 

I tracked on UPS and had the EMI RW&B removed before it got here, went to the computer & refreshed the screen, it said it had arrived, so I opened the door, and sure enough there it was! Took less than 15 min. to mount (versus 1 hr for the Eminence) T-Bolts just went right on in ! Anyway, plugged the strat in straight to the amp, clean chan
gain at 9 o'clock, vol @ 12 o'clock, tone @ 12 o'clock, and just played some of my usual noodles. The tonal difference was amazing. Very nice clean rounded tones, very well balanced tone range across all positions of the pickup switch, amd frankly I am impressed!

I have not pushed the volume up yet, and have not used the gain channel yet (I live in an apt. building and work 3rd shift so I have to pick my times to play loud) but I will update this soon. 

As of now I am very pleased with this speaker. It does have the 'halfway between Marshall and Fender' tone I was looking for, at least at this volume level. Further testing will of course be required.

For now, I'm one happy camper!


----------



## Arcarix

Update - Having played thru the Jensen more, and at higher volumes, it still sounds fantastic. The original stock speaker sounded just OK at first, but then quickly began to sound like a transistor radio speaker, if you know what I mean. It just sounded kinda 'cheap', like they put a speaker in the amp just because they had to. So I replaced that with an Emminence Patriot series 'Red, White, and Blues'. Unfortunately that spkr is 8 ohms, and rated for 120 watts. This amp is rated at 4 ohms, 50 Watts, so it lost some of the rated power driving into 8 ohms, and never really got pushed by the amps 50 watts which resulted in a ultra-clean sterile sound. 

So after installing the Jensen C12N-4 a friend of mine comes over to jam, and this guy already knows I mod my Strat a lot, but I didn't tell him about the speaker change. We start playing the usual stuff, and when we take a break he says "What did you do to the Strat this time, it sounds really good". He says "It sounds warmer, and I can hear all the notes." So then I told him "Nothing to the Strat, changed the speaker in the amp."

Point is, it's not just MY ears hearing the improvement, or just me wanting to hear a change, it's an actual, noticeable difference, and for me, it's a good one. 

So far I've cranked only the Clean Channel using a modded TubeScreamer, Boss PH2 SuperPhaser, and Boss DD2 digital delay with slight reverb from the amp. All the effects worked as expected, and were added one at a time after checking the totally clean sound. It all sounded really good.

Rent has just been paid, so in a couple of days I'll check out the OD channel, but since I'm really not much of a heavy metal player anyway my opinion of the sound quality of this spkr for that type of sound may not be of much value.

Please note that I'm not affiliated with the seller of this spkr, I just couldn't find any other 4 ohm 12" spkr anywhere, and all this LONG post is just my opinion, of course your mileage may vary.

As an afternote, I'm very lucky to have long suffering neighbours in my apartment building, and a beginner guitarist in another aptartment who plays LOUD, so when I play loud they are thankful that it's not quite as awful


----------



## shoelace

Hi,
I'm new here so sorry for the dumb question, but Peter, have you uploaded the schematics of your mods or not? Cause I didn't see them there but I'm dying to try them out.


----------



## holycowbatman101

I don't think he has .


----------



## Fixr1984

Here is a pic of my head. I did it awhile ago and thought I would post it.
The 2 controls on the far right are mid shift and bass shift for the OD channel.
I also added footswitchable gain boost.


----------



## shoelace

Won't you like to share that with us?


----------



## Fixr1984

shoelace said:


> Won't you like to share that with us?



Sure, its pretty simple. 
Take out C78 (bass cap) and C79 (mid cap). Replace those with wires. I used a little hot glue to keep the wires from bending too much and possibly breaking a trace.








I made a small circuit board to mount all my capacitors to. I Have 2 rotary switches mounted to the front. I used a 6 position for the mid and a 4 position for the bass.







Next step was to wire everything up. Little messy with the wiring but overall it worked out.


----------



## shoelace

Thanks a lot Fixr  I would gladly try this out, if you could only give me amount of caps needed (sorry for my English). And if it isn't a big deal for you, could you make some sound clips?


----------



## rockinr0ll

What is a mid and bass shift? BTW it looks very clean to me who isn't a mod expert.


----------



## Fixr1984

shoelace said:


> Thanks a lot Fixr  I would gladly try this out, if you could only give me amount of caps needed (sorry for my English). And if it isn't a big deal for you, could you make some sound clips?



I used 10 caps. 6 for the mid (one is a stock value) and 4 for the bass (one is a stock value).

Let me set my stuff back up and I will see about sound clips.


@ rockinr0ll. When you adjust the controlls on the EQ you are adjusting within a certain limit depending on what value capacitor you have. By adding different values on a switch you can basically "shift" the adjustable range of your EQ adjustability.
Not the best answer I suppose but I hope it helps explain a little.


----------



## shoelace

ok thanks, I'll be waiting but you still didn't say what amount caps you've used


----------



## Arcarix

Hey Fixr1984, that looks great, and easy to do also. By the way I believe shoelace is asking for the values of the caps you used, not the number of caps. Anyway looks like a nice neat install to me.


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## Fixr1984

Still working on the sound clips. 
To make it easier here is the layout I used. C2 is the stock mid value
and C7 is the stock bass value.


----------



## rockinr0ll

I can't wait to hear this thing!


----------



## Fixr1984

I havent forgotten, just having problems uploading at the moment.


----------



## shoelace

Still waiting


----------



## Fixr1984

Alright I tried to keep it simple. Playing is crappy, mic was crappy. Bass-5 Mid-0 Treble-5
You can hear when I change settings while the last chord is ringing out. This is the mid shift only I left the bass setting stock.



http://soundclick.com/share?songid=7419002


----------



## rockinr0ll

Cool, sounds a lot like when I add my eq to the amp. Are you going to do any more mods?


----------



## Fixr1984

rockinr0ll said:


> Cool, sounds a lot like when I add my eq to the amp. Are you going to do any more mods?



I would like to improve the gain boost. At higher volumes it's not as noticable.
Other than that I'm not really sure what I would want to change.


----------



## shoelace

nice mod but actually what I'm interested in the most is how to get rid off the buzz, which i like to call "the box effect" on the drive channel. Does anyone have any ideas where the problem might be?


----------



## RoydRage

Peter said:


> I can't understand why nobody has responded to this post - I took a really good amp, and significantly improved it. Another technician/guitar player I know who only plays tube amps made this comment to me when I was demonstrating the clean channel to him yesterday : "You would be hard pressed to tell it from a tube amp now". Wake up people. These mods rock.
> 
> PETER THE TONE DOCTOR



I'm WIDE awake Peter, I just read this now, and joined the forum because of It!

I have the AVT150H, with a 1960vintage Cab, and I love it!!! Very tube like!

I would like a little more GAIN, and a Heavy Weightier Sound, could you detail what exactly I would have to change for the tube mod, and tone mod... Not interested in having it pedal switchable..

Thanks,

Royd


----------



## RoydRage

So... 

I see Peter is MIA?!?

Does anyone have the details/diagrams for the gain, and tone shift mods that they can share

I want to get this implemented ASAP

Thanks,

Royd


----------



## rockinr0ll

He never gave any info... But a couple posts ups there is the bass/mid shift mod. I would suggest just getting an eq and putting it in the loop. That's what I do.


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## Fixr1984

RoydRage said:


> So...
> 
> Does anyone have the details/diagrams for the gain, and tone shift mods that they can share
> 
> I want to get this implemented ASAP
> 
> Thanks,
> 
> Royd




These mods are for the AVT50. You said earlier that you had a AVT150. You could compare schematics to see how interchangable these mods would be.


----------



## RoydRage

Fixr1984 said:


> These mods are for the AVT50. You said earlier that you had a AVT150. You could compare schematics to see how interchangable these mods would be.




Keen Eye there fixr... I knew I should have learned to read as a child!:eek2:

I was very excited I love this head, and I just drooled at the idea of a little more gain, and meat to the sound... Love that 80-81' Black Sabbath sound (mob rules, and heaven and hell).

Just bought a 79' 2203 off of ebay to get modded, but this AVT would be pretty amazing with some mods...

Thanks,

Royd


----------



## rockinr0ll

I was reading on another Marshall forum and somebody there mentioned that disconnecting the reverb on the AVT50 was a good mod. Thought I mentioned it, little was said about it but it sounds like it might give a boost to the signal or something.


----------



## Fixr1984

rockinr0ll said:


> I was reading on another Marshall forum and somebody their mentioned that disconnecting the reverb on the AVT50 was a good mod. Thought I mentioned it, little was said about it but it sounds like it might give a boost to the signal or something.



I wounder if they mean to simple unplug the tank or to bypass the reverb circuit on the board.

Do you have a link or remember where you read that?


----------



## rockinr0ll

He just unplugged. There is no more information so no need to post.

edit: but here it is anywayz

http://www.marshallampforum.com/forum/viewtopic.php?t=13554&highlight=avt

Could you try it and tell me how it goes? lol. I never really liked the reverb so I keep it low but with the amp being completely dry I don't think I would like that either.


----------



## rockinr0ll

fixr1984 do you have any more pics of the inside of the avt50 head? I have always wanted to see where the tube and reverb are located.


----------



## Fixr1984

Kinda far away photo...the pink arrow is the tube and the yellow arrow is the connector for the reverb tank.
I dont have a pic of the tank but its mounted on the top of the inside of the cab. If you look in thru the vent in the top you 
should be able to see it.


----------



## rockinr0ll

You know what, the AVT has a pretty nice layout. I'm kinda shocked that the tube is located on the board though. I always thought the tube would be facing up on top. I noticed you have the older one do you think that the avtx is the exact same or they made some slight changes? Also how easy is the Reverb tank to disconnect and have you tried it yet? And what preamp tube you using?

Thanks man for the pictures! I finally know what it looks like!


----------



## Fixr1984

rockinr0ll said:


> You know what, the AVT has a pretty nice layout. I'm kinda shocked that the tube is located on the board though. I always thought the tube would be facing up on top. I noticed you have the older one do you think that the avtx is the exact same or they made some slight changes? Also how easy is the Reverb tank to disconnect and have you tried it yet? And what preamp tube you using?
> 
> Thanks man for the pictures! I finally know what it looks like!




To disconnect the reverb just unplug the connector from the board (yellow arrow in the picture above.) I had played thru the amp with the reverb unplugged but I was testing the mid shift so I honestly cant comment on the effect of not having the reverb. I still have the stock tube in mine, its an Electro Harmonics.


----------



## Arcarix

I prefer to leave the reverb on 'cos I use it, especially with a Marshall Vibro-trem pedal for CCR tunes. With the Jensen spkr, the only thing I felt like I was missing for the fender type sounds was the vibrato a lot of their amps come with, but now I'm FINE! Seems like I've got the best of both worlds, anyway, sounds good to me!

Anybody have any thoughts on what tube to use for the pre-amp? Does it make any difference? Any preferences? I replaced the stock 'Marshall VLVE00065 WK45'with a JJ ECC83, and to tell the truth, I really couldn't tell any change in the tone. Any suggestions/opinions are welcome.


----------



## shoelace

Well, I've put a Tungsram NOS ECC83 in mine and I can feel the difference The marshall stock tube is quite dry and not that punchy. The Tungsram which I've put in has more character but it is a bit more noisy.


----------



## Arcarix

shoelace said:


> Well, I've put a Tungsram NOS ECC83 in mine and I can feel the difference The marshall stock tube is quite dry and not that punchy. The Tungsram which I've put in has more character but it is a bit more noisy.



Even with a strat I can deal with a LITTLE noise, (my strat has been copper shielded,single point grounded, grounded backing plates on all PUP's). How much did the Tungsram cost? 

Yeh the stock tube is pretty much just not 'there', like there's no real response, maybe 'dynamics' is the word I'm looking for. The JJ ECC83 I'm using now is just about the same it seems like. Replacing the stock spkr helped a lot, I just think the tube is the next major place for improvement.

I love this amp for the wattage (loudness), it's just right for home, maybe a little loud , but works very well in a small venue like bars, loud practice sessions w/drummer, studio is good, great all around amp, even at 60 pounds. 

I just feel like there's a lot more this amp can do tonally than what it does in the stock configuration. 

Thanks for your thoughts - anyone else?


----------



## lukeveess

Hello guys, do you know if it is possible to make the parallel fx loop on avt150h to be serial or to add a switch serial/parallel? if yes, how is it possible? thanks


----------



## cairomike

Hi. I'm new to this forum so I hope you might be able to help. I've been asked to service a AVT 50H, but don't have a circuit diagram. On the pre-amp board resistor R58 is showing signs of getting over heated. Measuring it in-situ it appears to be 15K, do you know if that's right?

You mention upgrading some components, which would you recommend for upgrade?

Where can I get a circuit diagram?

Thanks in advance for any help you can give me.


----------



## Fixr1984

Looking at my schematic it shows R58 as a 1/2 watt 10ohm resistor. I know this is a problem in these amps. (mine has been changed also) I would put a higher wattage resistor in to keep it from happening again. I believe mine is a 1 watt and it shows signs of getting hot. Send me a PM with your email address and I can send you the schematic.


----------



## eon

Wow, what a thread.

Im an owner of an AVT150 Head, and im wondering how these mods would work on that, as well.

Im also very interested in the Parallel to Series mod for this amp, to facilitate the use of a Boss GT-8's 4 Cable Method.

Anyone got any idears?


----------



## Fixr1984

eon said:


> Wow, what a thread.
> 
> Im an owner of an AVT150 Head, and im wondering how these mods would work on that, as well.
> 
> Im also very interested in the Parallel to Series mod for this amp, to facilitate the use of a Boss GT-8's 4 Cable Method.
> 
> Anyone got any idears?



I think it is possible they would work on the AVT150 as well. The component locations and possibly values will be diferent. I havn't seen the schematic so I cant verify one way or another.


----------



## mystic fred

I recently improved my AVT50 - I sold it and bought a JCM 600


----------



## shoelace

feel free to post your mods, cause I believe that many people, including myself, are eager to find out how to improve their gear


----------



## Fixr1984

I would also be interested in hearing what you changed in your amp as well. Was it a big improvement? Did it not help and thats why you sold it? My fan is making noise again so i have to open it up again so I wouldnt mind doing a few more mods.


----------



## rockinr0ll

mystic fred said:


> I recently improved my AVT50 - I sold it and bought a JCM 600



= sarcasm


----------



## Fixr1984

rockinr0ll said:


> = sarcasm





Wow............its been a long week. When I first read that I took it as he modified the amp and then sold it.


----------



## bellarum

You say that you did replace the 1/2 watt with a 1 watt @r58 and now it shows signs of overheating? or it did and now it doesn't? I just replaced the reverb pot that was stripped out on my atv50h and was looking around for signs of over heating on my board and found the orange-ish brown color on the board around r59 and r60. Could this have maybe been caused by the reverb pot being stripped out? r58 looks fine.


----------



## Fixr1984

bellarum said:


> You say that you did replace the 1/2 watt with a 1 watt @r58 and now it shows signs of overheating? or it did and now it doesn't? I just replaced the reverb pot that was stripped out on my atv50h and was looking around for signs of over heating on my board and found the orange-ish brown color on the board around r59 and r60. Could this have maybe been caused by the reverb pot being stripped out? r58 looks fine.



Yes, R58 was burned up and replaced with a 1 watt. The 1 watt resistor is starting to show signs of getting hot. R59 and R60 are part of the power section coming off of the transformer, doubtfull that is a result of the reverb pot. I see on the trace side of my board there is some slight discoloration on those 2 resistors possibly from heat. Do you have a picture of that area of your board?


----------



## bellarum

For some reason I didn't take a pic while it was apart. I will break it down again to do so, if it will help you out. The board isn't fried or anything. Just discolored at those points. When you say power section could that have anything to do with running a preamp like a POD XT in the effects loop? Or an EQ in the loop? I did both of those things at one time to sample them. Right now I have a BBE 482i rack mount Sonic maximizer,EH Holy Grail,Boss DD-5 delay in the loop. The reverb tank is unplugged and the knob is set at 4. Amp is running on the clean channel with a Boss NS-2,EH Metal Muff,Boss CE-3, and modded Boss GE-7 in front. With all of those running it sounds like I'm pushing it really hard. It sits on a stock 1960a JCM900 lead.


----------



## jfox00

Can anyone post a way to add a mid eq control for the clean channel of a Marshall AVT50H? Thanks.


----------



## rockinr0ll

Fixr1984 said:


> Wow............its been a long week. When I first read that I took it as he modified the amp and then sold it.



It's all good, just letting you know. BTW have you been doing anymore mods to the AVT? 



bellarum said:


> For some reason I didn't take a pic while it was apart. I will break it down again to do so, if it will help you out. The board isn't fried or anything. Just discolored at those points. When you say power section could that have anything to do with running a preamp like a POD XT in the effects loop? Or an EQ in the loop? I did both of those things at one time to sample them. Right now I have a BBE 482i rack mount Sonic maximizer,EH Holy Grail,Boss DD-5 delay in the loop. The reverb tank is unplugged and the knob is set at 4. Amp is running on the clean channel with a Boss NS-2,EH Metal Muff,Boss CE-3, and modded Boss GE-7 in front. With all of those running it sounds like I'm pushing it really hard. It sits on a stock 1960a JCM900 lead.



I also have a very similar rig (sonic maximizer in the loop and Boss in the front), I have had no problems. Chances are you are golden. 



jfox00 said:


> Can anyone post a way to add a mid eq control for the clean channel of a Marshall AVT50H? Thanks.



I use a 2 band EQ in the rack to get the needed mids. TBH I actually have been scooping the mids recently. On the clean it doesn't sound that great with mids, it actually distorts in a weird way.


----------



## Fixr1984

There's another thread about unplugging the reverb and using the reverb controll
to alter the sound. I did that but I am still unsure if i like it without the reverb on a little. I am thinking of making reverb footswitchable.


----------



## rockinr0ll

Yeah, I actually mentioned that a few posts back. lol.


----------



## VintageTone

Hey im looking for a avt 50 head, cant find one anywhere!!
i heard a very simple mod is to unplug the reverb, from inside
this is surposed to improve the amp


----------



## tgifntx

Chunked this in here hoping I'm in the right neck of the woods..? Have an AVT50h and was curious if somebody could tell me what the ideal scenario is or would be as far as cab/head match up in terms of ohm load proficiency. The head states, "minimum of 4ohms", And the cab I'm using is a 16ohm config. Is there an _optimal_ in terms of sound produce where *the two would best *match up? ie; 8ohm head/8ohm cab or 16ohm head/16ohm cab or even 4ohm/4ohm? How does or would this particular head best perform. Sorry for the long winded question and I thank you for any and all assistance.


----------



## Fixr1984

Honestly this question will probably get a bunch of different answers based on prefrence. The Head is rated at 50 watts into 4 ohms, so if you are running a larger load on it you wont get the full power. I'm not sure how much is lost going to 8 and 16 ohm. Half? Personally I would like a 4 vs 4 ohm so I could get the full power out of the amp. I have the 4x12 AVT cab and its rated at 8 ohms so I guess if Marshall paired them up this way then its no big deal. Tube is another story, you have to match the ohms to the amp or you are looking for trouble but on solid state its not too much of a concern.


----------



## Hawk

Fixr1984 said:


> Tube is another story, you have to match the ohms to the amp or you are looking for trouble but on solid state its not too much of a concern.



You sure about that? My understanding is that on any amp if you connect speakers in parallel you reduce the total resistance the amp sees, and the current through the amp increases. Take it far enough and you will fry something. key formuale are 1/Rtotal=1/R1+1/R2+1/R3.... and P=RxI^2

So if your amp is rated for 4 ohms and has a 4 ohm speaker, and is a 100 watt amp, max current would be sqrt(100/4)= 5 amps. Add a second 4ohm speaker and your total resistance drops to 2 ohms (1/R=1/4+1/4=1/2, so R=2ohms) and I=sqrt(100/2)=7 amps, nearly a 50% increase in current.

Correct me if I'm wrong, but that's my understanding of it.


----------



## rockinr0ll

The AVT cab is rated 8 ohms so that paired with another AVT cab (full stack) that would equal 4 ohms.


----------



## tgifntx

_Here's what it states in the manual_,
WARNING:
Always provide the AVT50H with a load
equal to, or greater than, 4 Ohms. Using the
two loudspeaker outputs, with cabinets rated at
8 Ohms each, the full 50W of the specially
designed AVT power amplifier will be
unleashed.

What I've done is, Using only one of the avt50h speaker outs
going into an 4x12 cab rated at max input 280W RMS/16 Ohms.
Am I in essence choking the amp or maybe the amp and cab?
Would I be better off to;
*A*. Rewire the cab to an 8 Ohm config
*B*. Rewire the cab to an 8 Ohm config and add an additional
spkr jack out to use both spkr outs, (L&R), so to speak from the avt
50h to "unleash" the avt50h...
I did check the Ohms on both the cab and the avt50h. The cab shows
16 Ohms, (single spkr out) and each of the speaker outs from the head
show 19 Ohms..?
Sorry to bird dog you guys... Just want to make sure I'm not matching
this stuf up all wrong.
Thanks again!


----------



## rockinr0ll

You have the matching AVT cab right? Then you are fine if it is.


----------



## tgifntx

No sir, Just an Eminence loaded cab unfortunately...


----------



## dsiar

You ARE the AVT50 man, I see, so do you know if a volume attenuator work with the AVT50? I realize that these devices are meant for tube amps but since the AVT50 has a preamp tube, I was wondering. Thanks, Dave


----------



## ddaypunk06

Hey guys,

Just finished reading all the posts in this thread.

Lots of info! Let me tell you lol.

I would love to eventually mod my AVT50Combo. I was wondering if Peter ever posted his website or anything involving the kits.

I just bought it less than a month ago. The guy I got it from on eBay spent 40 bucks shipping it and when it got to me it has a diagonal dent running through the two jacks on the right side of the unit. You can definitely see that the fron panel doesn't line up right. However I had to guitar buddies play on it and said it sounded great. The only other concern I had was that tonight after practicing a bit and writting...I noticed I could hear the fan when I turned it on. Being a sort of computer tech, I know buzzing fans ins't a good thing. I'm hoping that is an easy fix.

Some guys and I just got a band together and I am trying to see how easy it would be to mod this to get some more out of this amp.

Currently I play a squire strat (stock) on it (looking to get an Epi LP Standard Plus soon) and an older Gretch Electromatic. My amp before this was a 10W crate...sounded like crap. Thought it was my squire, but was definitely the crappy amp. Sounds great on the Marshall.

My buddy is going to revamp the wiring and pickups on my strat, and then I will also pick up the Epi LP.

Anyways, back to the topic.

I just want to get the true marshall tone with a bit more crunch in it. The mid mods sounded enticing as well. Possibly upgrade the speaker down the line too.


----------



## jjvh66

WOW nice mod on the AVT50. Is there a mod to make the clean channel CLEANER? I'm not quite using the gain as much nowa dayz.


----------



## rockinr0ll

dsiar said:


> You ARE the AVT50 man, I see, so do you know if a volume attenuator work with the AVT50? I realize that these devices are meant for tube amps but since the AVT50 has a preamp tube, I was wondering. Thanks, Dave



You are not suppose to use attenuators with Solid State or Hybrid amps.


----------



## rockinr0ll

jjvh66 said:


> WOW nice mod on the AVT50. Is there a mod to make the clean channel CLEANER? I'm not quite using the gain as much nowa dayz.



The only way I have found is to lay off the gain and boost the volume as much as possible. I can get a decent clean sound but like you said not as clean as I would like. You kinda have to sacrifice low gain with lower volume or crunch and a louder volume setting.


----------



## tgifntx

Woohoo!!
Gents...
I finally got the matching cab for my AVT50H.
No more goofin' around, On the money. Picked
up this AVT412B cab yesterday evening...


----------



## rockinr0ll

very nice


----------



## rockinr0ll

Question.

I have never went inside the AVT50HX. I'm planning on buying a new tube to replace with the old one. To change the tube I would have to open the back and then unscrew the chassis right? Can anyone give me any safety tips? I have done with before with tube amps but these hybrids seem a little more difficult to break into.


----------



## Fixr1984

Just unscrew the back, no need to take the chassis out. Pop off the wire hold down and pull the tube out. I wouldnt worry as long as you have the power disconnected there shouldnt be any hazzards for you.


----------



## rockinr0ll

What's the wire for?


----------



## Fixr1984

You can see in the picture, there is a stiff wire bent around the tube to hold it in place. Just slide that off and the tube can be removed.


----------



## rockinr0ll

Thanks for the help! I'll let you know how my experience turns out.


----------



## rockinr0ll

So my new tube is expected to arrive Tuesday. A few moments ago I decided I would open the baby up to take out the old tube and check out the internals. Lucky I had a good screw driver which made opening the back really easy. Pulled the wire out like you said and pulled the tube out, no problem what so ever. Put one of the screws back on and am just now waiting the arrival of the new tube. Thanks!


----------



## Fixr1984

While you wait you can unplug the reverb and see if you like the change it makes.


----------



## rockinr0ll

I'll try it out when I get the new tube. Too late to play right now.

e1: The reason I will most likely keep it disconnected is because most rack units are meant to be used before reverb, so keeping it on would not work.

e2: 12 hours from now I should have it, expect a follow up of my findings!  

e3: It's here!!


----------



## rockinr0ll

It arrived around a hour ago. The NOS JAN Phillips 5751 preamp tube made a world of change for my AVT50HX. Not only does it now have almost zero noise, it also has some added quality too. The reverb when switched off sounds great. It has a tone pot effect that when you turn it up the high frequencies increase. This is now how I have it set up. The amp sounds like a new amp!


----------



## Fixr1984

Sweet, where did you get the tube from? Price? Did you notice a change on both channels or more one than the other.


----------



## rockinr0ll

Got it Here, I paid the extra $4 to make sure I got a low noise and microphonics tested tube. 

U.S. Made JAN Philips 5751


----------



## rockinr0ll

The overdrive is less noisy. It went from really loud to almost dead silent.


----------



## ki6up

jfox00 said:


> Can anyone post a way to add a mid eq control for the clean channel of a Marshall AVT50H? Thanks.



Hey - I got a behringer eq-700 and ran it through the effects loop - what a differance. Other then a plastic body - it is as good as I have seen - you can adjust the clean perfectly


----------



## ki6up

jfox00 said:


> Can anyone post a way to add a mid eq control for the clean channel of a Marshall AVT50H? Thanks.



Hey - I got a behringer eq-700 and ran it through the effects loop - what a difference. Other then a plastic body - it is as good as I have seen - you can adjust the clean perfectly


----------



## rockinr0ll

I do the same ki6up!


----------



## rockinr0ll

Came across this today:

[ame=http://www.youtube.com/watch?v=zj_oIenTquE]YouTube - Marshall AVT Trick[/ame]

Kinda cool..


----------



## rockinr0ll

If anyone is interested I started a message board for the Marshall AVT.

Here is the link if you guys want to try to get a following...

Message Board - Home


----------



## Fixr1984

I signed up, now I just gotta remember to check in there along with the 4 other forums i use.


----------



## Johnfender

HI, I am new to the forum but maybe you can help me I purchased a used JCM 800 super lead 1959 model and I think I made a mistake, there is no way to control the volume on this beast...Have you heard or know of a Master volume Mod for this amp....


----------



## rockinr0ll

John this really isn't a good spot for the question you asked because not many people read this thread for mods on other amps besides the AVT. Try starting a new thread.

Fixr thanks for signing up. It could be a cool forum if people are interested.. Even though I made it, I don't really want it to be "my forum" I just made it because there is no sites dedicated to the AVT.

http://marshallavt.proboards.com/


----------



## wammi

You guys seems good with questions so if I may ask...

I have an atv50H head that has no reverb. Does the footswitch jack in the back turn it off and on assuming I had a footswitch? Maybe it came with a 2 button footswitch originally? Does anyone know? But I would think the reverb would get employed anyway when I turn the depth knob. Am I wrong?

Thanks for your help.
Wammi J.


----------



## Fixr1984

The jack in the back is just for changing the channel. Unless the depth knob is all the way down the reverb is always on. 
Have you had the head since new? If not check that reverb tank is still connected to the circuit board. Some people disconnect the tank as a mod to the amp.


----------



## wammi

Does anyone have a schematic? Also can anyone tell me (while looking at the back of the amp) which side the red reverb tank the rca is on (left or right), and what color wire is pin# 1 at the reverbs 4 pin plug on the board?
All seems tight, but I wonder if it is on correctly.


----------



## Fixr1984

I can email you the schematic if you need it.
Here is a few pics to hopefully help you out.


----------



## simmons1989

Peter said:


> I came up with some great modifications for my AVT50 amp:
> 1. The obvious mod: add a second speaker jack.
> 2. Installed a clean channel midrange control.
> 3. Increased preamp tube gain by around 25% (switched).
> 4. Installed a 6 position mid shift switch on the Overdrive channel with the stock midrange frequency, and 5 others [a great mod in any amp].
> 5. I reinforced some key components in the amp with higher wattage and voltage components (cheap insurance).
> 
> The *fatter tones *from the mid shift switch along with the *extra tube drive *really really brought the amp to life. The amp sounds 100% way better, and I didn't even drive the tube nearly as hot as in other tube amps. The clean channel tube sound really rocks on full gain, and rolls off at lower gains. Very impressive improvements. I am also working on an optoelectronically controlled footswitch for Lead Boost and Scoop. Anybody out there interested in Kits? I am interested in producing them.
> 
> PETER THE TONE DOCTOR


Cool mods, just wondering if you have any mods for the AVT150h?
Thanks.


----------



## brassriot

So I've got a burned out R58 and I wanted to know whether I should just replace it with the stock 1/2W or will putting a 1W prevent it from over heating again? Plus I'd like to know what "cheap insurance" Peter was talking about. I've got this thing all taken apart so if there is something I can do to beef it up or help prevent its over heating that would be nice. Also I'd like to know how to get more gain out of this puppy. I play out of a full stack and I play this sucker loud, so I can imagine why it gets so hot. 


Here are pictures of the burnt out R58 and the wear it made on the back of the PCB (which the discoloration is actually under R59 and R60 but the look fine themselves, maybe they might need to be changed as well?)

http://i80.photobucket.com/albums/j187/brassriot/burnout.jpg
http://i80.photobucket.com/albums/j187/brassriot/R58.jpg


----------



## Fixr1984

My R58 has been changed out already and it gets pretty hot. Personally I would put in a higher wattage. I dont have a technical reason I would just feel better knowing that the stock one burned up and the replacement gets hot. "cheap insurance", I have no idea. Maybe higher wattage components or better quality caps? For more gain check out the AVT forum I have a quick write up there, or I can PM you more info.


----------



## brassriot

so I changed out R58 with a 1w 10ohm resistor and it got ungodly hot almost 400 degrees f!! Something went pop and now there's hardly any sound coming out of it (only when I play the guitar hard.) It's making a funny noise right when I turn it on too. It doesn't look like the tube is lighting up all the way (maybe blew the tube?) and the leds that tell you which channel its on aren't working anymore. The CD Jack still works. I changed out R58 for its stock value hoping it would work but its still boned  help!


----------



## Fixr1984

Does the fan still work? My memory is slowly coming back to me: I'm thinking that the fan died in mine overheating the power chip and took R58 with it.


----------



## AVTMAN

Hi there avt fans ! I have been watching this avt50 forum to see if peter is going to give pricing for the diy mod kits. I recently made my avt slant cab stereo and am now looking for the next signifigant mod for my half stack avt. Anyone else out there with interest should post and make it worth his while to do kits.


----------



## Fixr1984

I dont think Peter has been around in a while. Check back to page 3 I have some info and some pictures that might help you out.


----------



## brandoz28

thanks for those pics man. hopefully the combo's are similar.


----------



## Peter

Hi, I started this thread, with the intention of producing kits for the AVT50. My amp is really great, but I came to the conclusion that doing the kits isn't worth it to me. Anyone wanting theirs modded in the Toronto area can contact me through my web site at ToneWerkz.com Musical Equipment Service, Mods, Repair, Kits, Forum Home Page , or at service@tonewerkz.com. Thanks.

Peter
The Tone Doctor


----------



## El Toro

Hey Peter. Saw your post and your surprised post that no one shouted back. So talk to me. I have a Valvestate 2000 AVT50 combo and I have tons of questions and would love to hear all about your mods. I'm an Industrial Electrician and was formally trained by the U.S.Navy in avionics so I should be able to follow you. I actually landed in this forum 'cause I was looking to find out what kind of preamp tube is used in the thing. Mine is marked simply with a 0041. Doesn't sound like an AX7 or EL84 so I was wondering what it is and does it cross. Thanks for the info,

Mike


----------



## brandoz28

it should be a 12AX7......pretty sure that's all they used in those

glad to see you're back around Peter


----------



## prodanov

Hi everyone!

I have a problem with my AVT50X. Maybe you can help me.

Problem #1. When I increasing gain on clean or OD channel volume also grows up. So if I want to play with high gain I have to put down volume almost to zero or I become deaf =)

Problem #2. The Reverb acts really strange. It doesn't give nice spring reverb to my sound but only cuts high freqs.

Any solution?


----------



## jgearhart76

Wow, I'm really bummed that Peter kinda dropped out on this. I joined the forum because of this thread.

I Have and AVT50H and was wondering how I could mod it. It has always sounded too bright in my opinion. Also the idea of a mid control on the clean chanel, and getting it to sound more like a tube amp intrigued me. 

Does anyone else have any suggestions/mods of their own?


----------



## jgearhart76

Fixr1984 said:


> I would also be interested in hearing what you changed in your amp as well. Was it a big improvement? Did it not help and thats why you sold it? My fan is making noise again so i have to open it up again so I wouldnt mind doing a few more mods.



My fan is having the same issue. Amp works great, but the fan has gotten noisy over time. is there a fix/treatment for this?


----------



## jgearhart76

Fixr1984 said:


> Honestly this question will probably get a bunch of different answers based on prefrence. The Head is rated at 50 watts into 4 ohms, so if you are running a larger load on it you wont get the full power. I'm not sure how much is lost going to 8 and 16 ohm. Half? Personally I would like a 4 vs 4 ohm so I could get the full power out of the amp. I have the 4x12 AVT cab and its rated at 8 ohms so I guess if Marshall paired them up this way then its no big deal. Tube is another story, you have to match the ohms to the amp or you are looking for trouble but on solid state its not too much of a concern.



I used to run my head through an 8ohm 4x12 cab and got plenty of volume out of it. (though not quite enough to cover my bassist! lol)


----------



## Jigz-RigZ

hey Peter, fist post! i have the AVT 50 H i love it but i dont! hahaha, you were recommended to me by Rob Hull at TubeDepot.com, im totally interested in the mods man, do yo have one to add more tubes?


----------



## jgearhart76

Looks like few have returned to this thread since last I left.

Just wanted to post an update. I did the Boost mod on my AVT50H, and it made a noticeable difference.

The clean channel is now more punchy and it will break up sooner when you crank the gain.

The Lead Channel sounds more beefy and compressed, almost as if there was a boost or an overdrive pedal in front of it. Cranked the gain to full and was amazed at the difference!!
 
Thanks to everybody on this board that helped me out!!


----------



## mturda

hi to all, i'm new here. i have avt50 combo, i tried the gain boost and its really good option to have but i am really interested on adding clean channel midrange control. does anyone have a schematic for it?

thank you in advance


----------



## Rockerduck

I know this is an old thread, but it started out with a speaker question, then mods, then nothing.


----------



## Rockerduck

I was wondering if anyone actually blew the stock speaker on a Marshall avt combo? I saw where "Peter" did a couple of years ago, hence his mods and the long thread.


----------



## Rockerduck

Wow, it looks like over a thousand viewed this thread after I posted a couple of days ago.


----------



## JoBur

Hey folks! I have the AVT50X Combo, and the Accutronics reverb tank went on it a second time. Why? I am super careful with all my gear. The serial number on the tank, 8db2c1b, suggests that it's a horizontal mount tank, but, it's mounted vertically, along the right side. Thoughts? Does that look like the right serial# to you? Last letter is hard to make out. Thought improper mounting could be the cause or the reverb to keep going. Also, which way does the plug go back onto the circuit board? In taking it off, I thought it would only go back on one way...I was incorrect. Thanks!


----------



## Rockerduck

If I remember, back a few responses ago, somebody said they moved the reverb tank as it was too close to the speaker and was pulling the springs in. I have an AVT50 combo and haven't had a thing go wrong with it yet. I'm going to put a V30 in it tomorrow and look at the reverb tank and see what up.


----------



## JoBur

Rockerduck. Take a look at your serial # on the tank, as well as the placement for me. I really wish I knew why mine keeps going. May have the wrong tank in mine, or could be improperly mounted. Who knows. I can't find a tech around here to help me out. Times like this, I miss being in NY where I had knowledgeable technicians on hand. Thanks.


----------



## Rockerduck

I actually have some old reverb tanks in my closet from Fender amps. They are about the same anyway. I save parts. Since I'm a tinkerer, I'll try something else to see how it sounds.


----------



## Capt Vemo

Hey Peter I have this same amp and I love it stock I would love to hear yours with the mods. Do you have any soundbites of it? Have you ever plugged it into a 4X12 cab? I did and it makes all the difference in the world. I also seen that you used a 4ohm speaker in it which marshall didnt reccomend using anything under 8ohms for that amp. It says on the back dont use anything under 4ohms but in the manual it says to keep it above 8 ohms. I want to get a cab with the G12H-30 70th anniversary speakers in it. But I have yet to hear those speakers with this amp.


----------



## Rockerduck

If anyone cares, the Vintage 30 I put in doesn't sound as good installed in the AVT50 as it does in a cab by itself. The OEM speaker went back in as it is designed for the space inside the AVT50. It hasn't blown yet anyway. I have a couple of Jensen's to try.


----------



## JoBur

I care. I thought about changing out the speaker for a v30, but was advised to stick with what I have. Glad I did. I think the stock sounds great. They were designed for that amp, no? I do wanna look into a better tube, if there are any suggestions out there.


----------



## Rockerduck

I'm not sure about tubes. I still use Sylvania tubes I've saved over the years when they were USA made. I'd like to hear from someone whose changed tubes and what difference it made. I have 3 AVT's, and none have needed a tube yet.


----------



## brandoz28

i put a Groove Tubes 12ax7 in mine, it smoothed out the sound and took a little of the harshness out of the top end.


an MXR 10 band eq does AMAZING things for these amps


----------



## Rockerduck

I agree. EQ's seem to be forgotten among all these players wanting to change their speakers out. I have used them over 45 years to tailor the amps sounds and I've had a slew of amps. Back in the day you had to deal with whatever came with the amps and you couldn't "mod" anything.


----------



## JoBur

Anyone wanna post a picture of their AVT50 combo, back open, for me? I really need to get a new reverb tank, but think mine may be mounted incorrectly. If no pic, a serial number may help. The number on mine suggests it should be mounted horizontally, but it's mounted vertically. Thanks.


----------



## eddiemacdaddy

I have a AVT50H and it does not have a fan inside ,is it possible to slice in a low watt fan in the head cabnit? also my R58 resistor for my reverb burnt up too, what size is that resistor? Oh and I will stick with the stock one ...lol....thanks


----------



## Fixr1984

R58 is a 1/2 watt 10ohm resistor


----------



## eddiemacdaddy

Fixr1984, thanks for the resistor imfo,


----------



## Whitey

I have an AVT 275, replaced the original Marshall 12ax7 with a Groove Tube. The clean channel has more headroom, slightly more gain, and a little more sparkle. I'm happy. (For kicks, I put the original Marshall tube in the V1 spot on my Peavey Delta Blues (also a 12ax7) and it blew in 2 seconds. Even the glass broke! I have no idea why)

Problem: I bought the amp cheap knowing that both the OD channels have to have the master volume cranked just for bedroom volume. I don't see anything burned out on the circuit board, but could have missed something. Any ideas what the problem might be? (not wanting to hijack but I didn't get much attention when I started a thread) thanks.


----------



## fief1999

Hello, I have an AVT50H, I don't have the right schematics, on the one I have the power circuit is made with a TDA7293 and on my circuit board I have an LM3886... My main PCB board is ISS5. Can someone send me the correct schematics?
Thx


----------



## Clara

I'm convinced that this amp sounds better pushing 8 ohms instead of the 4 ohm stock speaker. The stock speaker has a nasty upper mid spike around 3K that is reedy and annoying. 

I plugged into a 2x10 cab with Jensen Neos 10-100 wired for 8 ohms and it sounded like a whole different amp. When I tried the amp with a speaker cab at 4 ohms the old shrill honky sound returned.

Removing the back panel changes the frequency response of the stock speaker and it sounds better, but not as good as the Jensen Neos. I finally settled on an 8 ohm speaker with the bottom 3" of the back panel removed for a slightly open back cab.

With the back panel mod I set the bass at 7 with mids at 3.5 and highs at 3 Anything above 5 on the high end is too shrill at high volume. 

The next thing I did is try different preamp tubes. The stock Marshall tube was a long plate Russian tube. Higher gain tubes tended to sound too harsh. I tried a slightly lower gain 12ax7c and that sounded better - smoother, warmer.


----------



## Jimloucifer

Hi Peter. You post some great ideas man. Thanks. I have an AVT 50watt head through a VS412 Cab. I tried that reverb detachment idea. (Adding a kind of makeshift presence to the reverb pot. I didn't really like the reverb on this head. So I thought that if you kept the cables connected to the mother board. Then you could use the converted RCA in/out jacks regular jacks. Easy to plug in a EQ, or some kind of effect instead of an unused reverb channel. Any thoughts on this? I would appreciate the input. Cheers


----------



## jjvh66

Can anyone post some audio of the boost mod, speaker swap (of any kind) and the open back panel?


----------



## iron broadsword

Well I can't post audio but I'll say this: Swapping the stock speaker is the only thing I think is really necessary to help this amp. The sound of it through a good speaker (G12T-75, V30, Greenback, etc etc) will probably fix anything you don't like about it. When I plugged my AVT150h into my 1960a instead of the AVT cab I had it sounded perfect.. just what I would want out of it.


----------



## BoogieRandy

I put a ported back and a G12t75 in mine. Check it out.


----------



## novoselpro

"Anyone wanna post a picture of their AVT50 combo, back open, for me? I really need to get a new reverb tank, but think mine may be mounted incorrectly. If no pic, a serial number may help. The number on mine suggests it should be mounted horizontally, but it's mounted vertically. Thanks."

JoeBur, mine is mounted vertically as well. I think they came that way.


----------



## 1964 ranchero

Hey
Interested in doing some mods to my AVT 50 H head. I'm into hard rock/ metal. what would you recommend and did you ever make any kits ? Thanks Harry


----------



## screamincheetah

New to this thread. I own both an AVT50H and an AVT50HX. I run a BBE Sonic Stomp through the effects loop of both amps. The Sonic Stomp really brings these amps to life. Not that they don't sound great stock, its just that the BBE adds sparkle and thump to these amps. Its like adding a presence and resonance control to the amp. 

BTW, the reverb went out on my AVT50H, so I run a Boss Reverb Pedal through the effects loop as well.


----------



## Porschester

Hey,

Anyone ever heard of putting a capacitor between the clean and the dirty so that the Volume difference doesn't cause so much of a pop when the footswitch is pressed?

Is such a mod possible? I have heard of a similar thing before, on YouTube one older guy added a capacitor to the female side of the input jack (inside the amp), this he said 'tames the pop' when the jack is plugged in or pulled out. It looked like a pretty small capacitor.

Can someone who knows electronics suggest where this would go (I expect somewhere close to the switch itself) and what rating capacitor I should use

This is all related to my other crackle/pop thread, link below.
http://www.marshallforum.com/workbe...-when-switching-clean-crunch.html#post1093386

Much thanks.

Added ... Check out this guys solution to popping .. http://www.analogman.com/faq.htm
I quote 
"Popping sound when effect is switched
_My effect with DPDT switch makes a "popping" sound when I switch it in and out. How can I quiet this down? _
This is caused by a change in levels between the effect BYPASS and ON modes. According to Geoffrey Teese (Teese Real McCoy wahs- the best wahs available) You can fix this by adding a 1 MegaOhm _tie-down_ resistor on the circuit board. You need to add it between the INPUT and ground. Do not add it at the jacks, but on the circuit board."


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## Clara

I have two combos - AVT50 and AVT20. To make this amp sound better I:
1) Got rid of the stock speaker and swapped it out to a good 8 ohm speaker
2) Open the back slightly - Two 2-1/2" holes or remove about 2-1/2 inches off the bottom of the back will work - cab still tuned low.
3) Plug a jumper (like you use betwen pedals) from the Emulated Out to Effects Return or if you have the AVT20 Emulated Out to CD In


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## adam183

rockinr0ll said:


> Came across this today:
> 
> YouTube - Marshall AVT Trick
> 
> Kinda cool..



i watched this few days ago...didnt take a note of the settings as i hadnt bought the amp, now the video has gone, so can anybody tell me what the 
trick is to get 2 extra distortion sounds from the avt's with the effects? 
i know its some thing to do with the flanger and the delay....

cheers

adam


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## HiggY

Please notify me when kits are ready
GBU
Higgy


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## Driver

Fixr1984 said:


> Still working on the sound clips.
> To make it easier here is the layout I used. C2 is the stock mid value
> and C7 is the stock bass value.



I know that this is an old thread, but I do this mod on my vs265 and have some questions.
It sounds great, but there is a problem: very loud "pop" sound when I swich from one to another capacitor. Do anybody know why this happens and how to solve the problem. Some grounding, or keeping the current in capacitors constant?

Thanks, and sorry for poor English


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## rx7carl

I know this is an old thread but maybe I'll get some help. I just got an AVT50h. Great amp, sounds great thru my 1960a cab. Classic rock tone and distortion is great. I do also play metal tho and would like info on the added gain mod. Didn't see specifics in this thread. My valvestate 90w combo does metal great with the contour knob control. Any help would be appreciated


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## rx7carl

Any help would be appreciated thanks


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## R33

Peter said:


> I can't understand why nobody has responded to this post - I took a really good amp, and significantly improved it. Another technician/guitar player I know who only plays tube amps made this comment to me when I was demonstrating the clean channel to him yesterday : "You would be hard pressed to tell it from a tube amp now". Wake up people. These mods rock.
> 
> PETER THE TONE DOCTOR


Hey man I want to fix my AVT 50 watt head just like yours How $ we're do I start mail it to you and pay you?


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## R33

R33 said:


> Hey man I want to fix my AVT 50 watt head just like yours How $ we're do I start mail it to you and pay you?


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## R33

Sounds like the perfect fix .How/ we're/ when $ much.


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## R33

I am knew so can I send my # email ? If I send amp and never see it again I don't care it's useless anyway especially after hearing you say what it sounds like now .maybe you could tell me we're to get parts and draw me some skematics.How much would that cost.I mean if one Marshall guy caint trust another .I am out


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## SkyMonkey

Hi @R33 and welcome to the MF 

This is a really disjointedly old thread.
If you hover the mouse pointer over the names of those who posted in the thread it will show you when they were last active.
All of those you have tried to attract the attention of haven't been seen for 4 years or more.

Sorry.


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