Slash AFD100 boutique amp (#34 and #36/39 in one amp)

Antônio S

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Hello guys. All right with you? Hope everything is great.

My name is Antônio and I live in Brazil and like you, I'm passionate about vintage electronics and tube amplifiers. I'm still at a low level of knowledge about amplifiers, but I've studied and already understand some things.

The reason for my visit here is that, recently, I ordered a tube amplifier handmade by an experienced builder here in Brazil. As a good Slash fan, I immediately opted to reproduce modifications #34 and #36/39 made by Frank Levi and Tim Caswell. After a lot of research on the internet, we gathered the schematics and chose to follow the Marshall AFD100 diagram and that's how my amplifier was born.

It has a few more “features”, being a 50 watt amplifier, with 2 EL34 Tung-Sol in power and 5 12ax7WB Sovtek in pre. It has hand-wound transformers, tube effects loop and 2 fully independent channels, with individual equalizer, master volume and gain for each channel. The first channel (clean) is based on Marshall Plexi, using the original diagram. The second channel is a JCM800, with 2 keys available that activate the mods, one key for mod #34 and another key for mod #36. When both switches are off, it is a standard JCM800.

My doubts are as follows:

1. To get the #36/39 (AFD) sound, does the switch on mod #34 need to be in the on position? Because activating only switch #36/39 and leaving #34 off, it seems that something is still missing in the sound. As soon as I switch the switch from #34 to on, the sound is identical to the AFD album.

2. Are Sovtek's 12ax7WB valves influencing? I know they are valves aimed at a darker tone and maybe I'm denigrating the real sound of the mods.

3. Is it worth changing the EL34 for 6550? In the Marshall AFD100 the valves used are 6550 and in Slash's own amplifier as well.

I hope you understood my doubts and I will be very happy if you can help me! I am attaching photos of the internal part of the amplifier and the schematic used for construction.

Grateful,

Antonio.
 

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Pete Farrington

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1 I suggest not to worry about that stuff, and to use to amp’s controls and switches to get the best sound.
2&3 Different designs of valves, and especially different valve types, do tend to sound a bit different.
If you fancy experimenting with 6550 / different makes of 12AX7, then go for it.
Otherwise, it seems that you think the amp can be set to sound great, so just enjoying it as it is looks to be a valid option.
Be aware that different output valves, and especially different types of output valves, should best be checked in the amp to make sure the amp is providing suitable conditions for them. One set of output valves may well require a different bias setting to another set. 6550 will almost certainly require a bias adjustment.
 

Leonard Neemoil

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I have no idea but it looks nice and welcome to the forum.

Seems like some good advice above.
 

Antônio S

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1 I suggest not to worry about that stuff, and to use to amp’s controls and switches to get the best sound.
2&3 Different designs of valves, and especially different valve types, do tend to sound a bit different.
If you fancy experimenting with 6550 / different makes of 12AX7, then go for it.
Otherwise, it seems that you think the amp can be set to sound great, so just enjoying it as it is looks to be a valid option.
Be aware that different output valves, and especially different types of output valves, should best be checked in the amp to make sure the amp is providing suitable conditions for them. One set of output valves may well require a different bias setting to another set. 6550 will almost certainly require a bias adjustment.
Thank you, Pete. I agree with everything you said.
Certainly the change from EL34 to 6550 will require a new polarization.
My doubt about the mods keys is to try to learn a little more about the amplifiers... my nerd side talking lol
 

Pete Farrington

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My doubt about the mods keys is to try to learn a little more about the amplifiers
Unfortunately, without the amp chassis on the bench in front of us, it’s very difficult to be sure how exactly switches are wired.
An email / text message / phone call to the builder is your best way of getting that detailed info.
Other than that, you or a local tech would need to use a meter to work out how the front panel switching options correlate to the schematic.
 

bassmastermkii

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Hello guys. All right with you? Hope everything is great.

My name is Antônio and I live in Brazil and like you, I'm passionate about vintage electronics and tube amplifiers. I'm still at a low level of knowledge about amplifiers, but I've studied and already understand some things.

The reason for my visit here is that, recently, I ordered a tube amplifier handmade by an experienced builder here in Brazil. As a good Slash fan, I immediately opted to reproduce modifications #34 and #36/39 made by Frank Levi and Tim Caswell. After a lot of research on the internet, we gathered the schematics and chose to follow the Marshall AFD100 diagram and that's how my amplifier was born.

It has a few more “features”, being a 50 watt amplifier, with 2 EL34 Tung-Sol in power and 5 12ax7WB Sovtek in pre. It has hand-wound transformers, tube effects loop and 2 fully independent channels, with individual equalizer, master volume and gain for each channel. The first channel (clean) is based on Marshall Plexi, using the original diagram. The second channel is a JCM800, with 2 keys available that activate the mods, one key for mod #34 and another key for mod #36. When both switches are off, it is a standard JCM800.

My doubts are as follows:

1. To get the #36/39 (AFD) sound, does the switch on mod #34 need to be in the on position? Because activating only switch #36/39 and leaving #34 off, it seems that something is still missing in the sound. As soon as I switch the switch from #34 to on, the sound is identical to the AFD album.

2. Are Sovtek's 12ax7WB valves influencing? I know they are valves aimed at a darker tone and maybe I'm denigrating the real sound of the mods.

3. Is it worth changing the EL34 for 6550? In the Marshall AFD100 the valves used are 6550 and in Slash's own amplifier as well.

I hope you understood my doubts and I will be very happy if you can help me! I am attaching photos of the internal part of the amplifier and the schematic used for construction.

Grateful,

Antonio.
V1 and V2 are the money tubes in terms of tone. I’ve been very far down this road. Yes, the tubes have a huge effect on the tone of a high gain amp. The 12ax7wb (sovtek I presume) are serviceable but not inspiring in my experience.

If I had to guess - I think the mullard CV400412ax7 (short plate) reissue is the tube you are looking for. It is the closest sounding modern production tube to the vintage Brimar ECC83 in my hearing. The short plate makes it tough enough for V1 to mechanically quiet.

The problem with the 80’s mods can be too much gain so “regular gain” mu value tubes are plenty good.

Another possibility with the jubilee is the clipping diode choice. This Is a place where subtle differences in gain can be had. However, mostly silicon, v led. I haven’t heard much difference in silicon but I can hear differences in LED by color and size. Check to make sure your clone (nice build BTW) was close to the original.

Cheers!
 

BRMarshall

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it seems you have a very cool amp - I can’t help with your technological questions though. I’m seconding others with enjoy playing through it and find the tones you’re after. Yea, try to reconnect with the builder or a tube amp tech you have faith in. Best of luck getting this sorted out.
 

Antônio S

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Thanks for the tips, guys.

I made some sound samples showing the different combinations of switches. It's nothing professional, just the iPhone's microphone right in the center of the speaker.

My cabinet is 2x12 equipped with 2 Celestion V30 MesaBoogie, manufactured in 1996 and the settings are:
Presence: 7
Bass: 4
Middle:5
Treble: 7
Gain: 7
Master: 2

Plexi Clean


JCM800 without mods


Switch #34 on and #36 off


Switch #34 off and #36 on


Switch #34 on and #36 on
 

ibmorjamn

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Hello guys. All right with you? Hope everything is great.

My name is Antônio and I live in Brazil and like you, I'm passionate about vintage electronics and tube amplifiers. I'm still at a low level of knowledge about amplifiers, but I've studied and already understand some things.

The reason for my visit here is that, recently, I ordered a tube amplifier handmade by an experienced builder here in Brazil. As a good Slash fan, I immediately opted to reproduce modifications #34 and #36/39 made by Frank Levi and Tim Caswell. After a lot of research on the internet, we gathered the schematics and chose to follow the Marshall AFD100 diagram and that's how my amplifier was born.

It has a few more “features”, being a 50 watt amplifier, with 2 EL34 Tung-Sol in power and 5 12ax7WB Sovtek in pre. It has hand-wound transformers, tube effects loop and 2 fully independent channels, with individual equalizer, master volume and gain for each channel. The first channel (clean) is based on Marshall Plexi, using the original diagram. The second channel is a JCM800, with 2 keys available that activate the mods, one key for mod #34 and another key for mod #36. When both switches are off, it is a standard JCM800.

My doubts are as follows:

1. To get the #36/39 (AFD) sound, does the switch on mod #34 need to be in the on position? Because activating only switch #36/39 and leaving #34 off, it seems that something is still missing in the sound. As soon as I switch the switch from #34 to on, the sound is identical to the AFD album.

2. Are Sovtek's 12ax7WB valves influencing? I know they are valves aimed at a darker tone and maybe I'm denigrating the real sound of the mods.

3. Is it worth changing the EL34 for 6550? In the Marshall AFD100 the valves used are 6550 and in Slash's own amplifier as well.

I hope you understood my doubts and I will be very happy if you can help me! I am attaching photos of the internal part of the amplifier and the schematic used for construction.

Grateful,

Antonio.
Welcome , that is a very cool looking amp from a controversial heritage. George lynch I believed also used the original before it disappeared on tour with Dokken close to the same time.
Anyway sounds like a good problem to have !
 

Antônio S

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Just to note that mode is slightly boosted compared to stock, due to the partial bypass on the last common cathode stage (0.68uF//820ohms). Also the high cap values on the gain control.
It actually seems to have a little more gain and brightness compared to a JCM800 2203 Marshall. Sometimes I feel like the bass is exaggerated...
 

Gblev

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If your trying to get the tubes to put you on the path for the #34 and #36 sound, Slash used 6550's in both amps. So stick with those tubes.

One key component that was missing from the AFD100, that was in both #34 and #36, is the hot-shield. This is a key part in getting those mods to sound correct. The length of the hot-shield plays a major role in the overall brightness of the amp, and it's also the main component for getting that 'wah-like' effect you hear with these mods. The AFD100 used capacitors instead of a hot-shield, and while this will give you that effect to some extent, it really does not sound like a proper hot-shield. I don't believe I see a hot-shield in your amp, unless I'm missing it? So this could be part in why you don't think your mods sound correct.

Just for the record. The infamous #39 that Slash used in preproduction was also done by Frank Levi and not Caswell. #36 and #39 are the exact same Levi mod. Caswell's #39 is something different, and was popular at S.I.R. in its own right before AFD era came around.

Your amp sounds good, and your playing is good as well. While it may not nail the Slash tones exactly, it is close, and very similar to the AFD100. Congrats!

I hope this helps.
 

Antônio S

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If your trying to get the tubes to put you on the path for the #34 and #36 sound, Slash used 6550's in both amps. So stick with those tubes.

One key component that was missing from the AFD100, that was in both #34 and #36, is the hot-shield. This is a key part in getting those mods to sound correct. The length of the hot-shield plays a major role in the overall brightness of the amp, and it's also the main component for getting that 'wah-like' effect you hear with these mods. The AFD100 used capacitors instead of a hot-shield, and while this will give you that effect to some extent, it really does not sound like a proper hot-shield. I don't believe I see a hot-shield in your amp, unless I'm missing it? So this could be part in why you don't think your mods sound correct.

Just for the record. The infamous #39 that Slash used in preproduction was also done by Frank Levi and not Caswell. #36 and #39 are the exact same Levi mod. Caswell's #39 is something different, and was popular at S.I.R. in its own right before AFD era came around.

Your amp sounds good, and your playing is good as well. While it may not nail the Slash tones exactly, it is close, and very similar to the AFD100. Congrats!

I hope this helps.
Thank you for your help! It sure was great.

I'm going to change the power and pre amp valves for 6550 and 12AX7, both from Tung Sol. I agree that they are key parts of Slash's sound.

About the hot shield, I really wanted my amp to have it, in fact I asked to be assembled with it! But no builder wants to do this type of assembly, they think it's too dangerous and that the capacitors do the same job.

You're right, looking at the story, both mods are done by Frank Levi, I think he called it a "kill mod" or something.

I'm glad you liked the sound! It really is very good, but it seems like 5% is missing.

My biggest doubt is in relation to the schematic of the switches, because to my ears, switch #34 needs to be active along with switch #36. I look at the schematic and try to understand the components, but I'm still pretty inexperienced in this area.
 

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Gblev

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Thank you for your help! It sure was great.

I'm going to change the power and pre amp valves for 6550 and 12AX7, both from Tung Sol. I agree that they are key parts of Slash's sound.

About the hot shield, I really wanted my amp to have it, in fact I asked to be assembled with it! But no builder wants to do this type of assembly, they think it's too dangerous and that the capacitors do the same job.

You're right, looking at the story, both mods are done by Frank Levi, I think he called it a "kill mod" or something.

I'm glad you liked the sound! It really is very good, but it seems like 5% is missing.

My biggest doubt is in relation to the schematic of the switches, because to my ears, switch #34 needs to be active along with switch #36. I look at the schematic and try to understand the components, but I'm still pretty inexperienced in this area.
I see a couple of differences there from the #34 schem and your schem's #34 mode. But it's possible that these changes are for the favor of your #36 mod. They are not big differences, but will change the sound a little. You have the plate resistor bypassed with a 410p cap (I'm assuming your cap value here is in pico farads) and in the #34 schem it's a 500p. That's not a huge deal. And the other thing I see is your cathode bypass cap here is a .68uF over the 820r, just like how it is in the AFD100, where it's a .47uF over the 820r in #34. The .68uF cap will give you a little more gain and has lower frequency cut off. Again, this isn't that big of a deal, just a slightly different flavor with a little more punch.

If I'm reading this correctly, it appears that all your 'B' switch is doing is adding the extra tube in the circuit, where 'A' is bypassing this part of the circuit. If that's the case, and I believe it is, your #34 is running when 'B,' #36 mode, is engaged. This is how it is in the AFD100.

The hot-shield is safe if done correctly. Marshall installed these in some of their amps coming from the factory back in the late 70's and early 80's. My '83 JCM800 had one.

I'm not 100% sure, but from what I saw in the videos for songs from Slash's new album, 4, he used his AFD100 for some of the tracks. It's sounds pretty good. Go listen to them on YouTube and it will give you a tone to shoot for and see how your amp compares. Of course, you could just look at some of the AFD100 videos people have posted for the same thing.

I hope this helps.
 

thetragichero

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that's a 470pf cap not a 410pf. 470 is just a standard value and with 10% tolerance caps is equivalent to 500pf anyway
 

Gblev

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I couldn't make it out too good, and thought it was odd, but went with it anyway. Yeah, that's not going to make any difference, and is probably within the tolerance of the 500p cap anyway.
 


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