B-52 AT-100 Tri Mode Rectifier Explaination...

damienbeale

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I don't disagree that the AT-100's Gain 1 channel is on the flat side (and honestly, that's the best description - it's just flat...). There's a lack of "roundness" to the tone - But, I find the same thing to be true in many amps. JTM 45 for one. Some guys love that amp - It just doesn't work for me. Doesn't mean it's a bad amp.

I don't think much of the 90's and onwards JTM45 re-issues, to be honest. They're not much like a real JTM-45, or a properly built clone.
 

charveldan

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The first time my tech biased that amp he remarked that it had so many transistors/diodes but on the front its labeled "all tube" ...lol.

Chris is a humbled guy but he didn't think much of the amp.

I wouldn't own another one, I was basically helping a long term friend who had money problems.
 

Rootwitch

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Did you pay $600 for a used one, or are you referring to the price of a new one?

Yeah, not sure I'd shell out $600 for a new one. At that price point, I'd likely look for something different. But $275, re-tubed a few months ago, with the channel switcher pedal... Easy choice. But again, I'm a pedal(s) guy, so I just need a good clean channel that doesn't mess with the tone of my pedals.
 

charveldan

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Did you pay $600 for a used one, or are you referring to the price of a new one?

Yeah, not sure I'd shell out $600 for a new one. At that price point, I'd likely look for something different. But $275, re-tubed a few months ago, with the channel switcher pedal... Easy choice. But again, I'm a pedal(s) guy, so I just need a good clean channel that doesn't mess with the tone of my pedals.
Guitar Center & Musicians friend were selling the first models in 2007 for about $700.

I needed a rack EQ, sonic max, rack processor and a bunch of pedals just to get decent basic rock tones.

I'm not much for rack stuff anymore, some pedals, a couple heads & cabs is all I want as long as they sound decent.
 

Marshall Art

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I know it doesn't really matter but I shiver when I see those tube sockets mounted in the circuit board. But hey the new 5153's are the same way right?
 

damienbeale

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Most amps are the same way nowadays. Nothing wrong with it, per se, provided there is some support for the tube sockets, ie. sockets screwed to chassis.
 

Marshall Art

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I bet it would suck if you ever had to replace a tube socket. Or for people like me who can't solder good.
 

Vail Ave

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I see this thread is pretty old but thought I would offer my experience with the B-52 AT-100. I guess I should qualify myself here. In the last 10 years, I have owned about 28 tube heads, Mesa, Marshalls, Fenders, HiWatt, Randall MTS. I play a Les Paul Custom for high gain tones (Tool, Chevelle, Deftones, Metallica, etc) and a Strat for blues (SRV, KWS).

I'm also involved in the electronics industry and love tinkering with tube amps. As such, I bought my first AT-100 for that purpose, to mod and tinker with for fun. So I will second the motion that has been made in this thread, these things are dirt cheap. Over the last 5 years that I have owned B-52s, i can not imagine having more fun on 300 bucks. I now have 3 of them, but typically have 2, my main experimental amp, and one extra. I normally try new circuits on my experimental amp and break them out on switches or pots, once I get the tone I like, I then hardire the winning circuit into the second amp.

A couple quick points or pros and cons about this amp.
Bruce Egnater designed this amp for B-52. In my opinion, he did an excellent job and from a schematic perspective, this would be my signature amp. The preamp are really where the magic happens in this amp, the power section is where the improvement can be made.

The clean channel is almost exactly a Fender twin pre. Sounds awesome. No complains. I have not done anything to the clean channel. If a mesa clean channel sounded this good, or took pedals this good, it would raise mesa's loyalty I think.

The overdrive channels are a Marshall jcm900 circuit hot rodded with an extra gain stage. But, the really great addition that makes this 10x better than my DSLs is the contour switch. Most people call this amp a poor man's mesa (recto), but in fact, the tube rectifier is the only feature even close to a mesa amp or circuit.

Pros:
1. Very inexpensive
2. Sounds great, more Marshall than a Marshall for me.
3. Very versatile. Clean, blues, metal, it sounds really good for all without a consession.
4. Tube rectifier. I like alot of sag. I'm addicted to tube rectified amps when playing high gain.
5. 3 channel. It is actually a 2 channel, and the high gain channel has two modes.
6. Exceptional clean channel.
7. Higher gain amp. Plenty of gain.
8. Sounds great with a Les Paul or a strat. This might seem like a silly thing, but it isn't. You simply can't play SRV on a Recto in stock trim.
9. Switchable effects loop that switches on the return side. This allows a ton of cool hookup options, my favorite of which is to use an offboard preamp and when you switch on the loop, you are now playing an entirely different pre over the b52 power section. Especially handy for JMP-1 or ADA MP-1 users.
Cons:
1. Heavy
2. According to some tube experts that help me out every so often, a single 5U4 Recto tube is only good for 50 watts, and the amp will roll off the bass hard trying to rectify 100 watts with only 1 tube.
3. Build quality. I think the build quality is great considering the price point. You will not gain much by replacing any components except maybe little less noise. But I do agree despite my love of this amp that it could be so much better. The power section does sound a bit anemic sometimes.

Now the good stuff. I have modified 47 circuits learning and having fun. Of that, I have reversed all but 5. The most important one of all is the addition of a presence control on the high gain channels. No matter what cab I use, both with a strat or a Les paul, this amp was bright. Very bright to my ears. So I took a preamp based (not negative feedback) presence control circuit out of a mesa schematic and it worked magic. Then, to address the green channel or channel 2 thin ness, I jumped the extra gain stage so that the 2nd and 3 channel had the same tube stages. I run channel 2 in lower gain for blues, but this mod fattened channel 2 way up.

As I said, I like alot of sag. So, I always have this in tube recto mode. I also have the resonance knob at 0 to keep the power as loose as possible, no damping. This does result in the amp having less bass. My solution is to play it through my mesa oversized cab, or an old ampeg cab I have that is oversized with swamp thanks in it. If you are playing it through a marshall cab with G12-T75s, I could see how it would be unbearable, bright with no bass.

I love these things. If you have one and want to mess around with it, here are some fun things to do.

1. I do think the power section is where all the money was saved, but I can not put my finger on what exactly an improvement could be. I have though about replacing the filter caps with "better ones", but modern electrolytic caps are not really that different. Trannies would be a good place to start, but I like trying super cheap stuff instead. Perhaps the KT tube change mentioned here would be interesting. I have a big trim pot for bias on the outside of the chassis now because I used to change tube so much. But, the point is, I know the amp can sound better because of this fun trick. Take a cable and plug into the effects send of this amp, and plug you guitar into this amp. But take the cable out of the send and plug it into the return of a different amp. This is what I do if I want to know what would happen if I had the pre from one amp with the power section of a different amp. If they both have an effects loop, it is easy to find out. Especially cool if you have different tubes in a different amp, like E34Ls, or KT88s. Anyway, when I run the effects send of the b52 into the return of my Triple Rectifier, whoa! It sounds great, awesome. Likewise, when I record, I take the signal out of the effects send out of the amp, into a cab simulator, and directly to the board. It sounds awesome. This tells me two things. 1. This amp is worth having for the preamp alone. 2. There is room for improvement in the power section.

2. If you have an EL-34 based amp, or just want to hear what your DSL would sound like over 6L6s tube rectified do the same trick. Take effects send out of your other amp, and into the return of this one. Tube rectofier on, engage the loop, sag city. When you do this, set the master to 0 and plug an impedance matching load resistor in the amp you are pulling the preamp signal from.
 

Vail Ave

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With all that said, there is in fact a better amp out there these days in this low buck price point. The Jet City JCA 50 and 100 heads. Mine is great quality and sounds amazing. It is a simpler, higher quality product out of the box than the b52. I bought mine used to tinker with and mod and I played bone stock for 2 years without touching a thing. I finally just changed the Chinese branded power tubes last week and it does sound better with Sovteks in it. I will likely do the depth mod to see if it will work to my liking, but it is a great amp, and if you can only have one gigging amp to play with, I would probably go with the jet city over the b52.

I have also been on an Ada MP-1 preamp kick for sevreal years. The MP -1 is my go to amp now, and probably forever (running into the effects return of my Triple Rectifier.)
 

kladmin

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I know this is an old thread, but I want to share my experience having used this amp gigging 4-8 times/month for the last 6+ years.

In my opinion the durability is fantastic for what I paid for this amp ($500 w/ B52 4x12), in fact, it went off the back of a raised stage (along with the 4x12 cab and a girl lol) and simply had to be returned to the stage and plugged back in. Got some minor dents on the back and broke the speaker jack that had been in use, but there are two speaker jacks ;)

I never have used the dirt channels, they didn't do much for me, but neither do the dirt channels on pretty much any amp I have played. I pretty much always use pedals for OD and distortion.

I currently own a Fender Twin Reverb, Mesa Boogie DC-2, Fender 5E3 clone, and a souped up Fender Champ. This amp is the one I gig with!!

The clean channel is supposed to be a copy of a twin reverb and it sounds like it, although sonically to me it seems to have more of an edge or modern character which I love. I have done entire blues shows with this amp and entire rock/metal shows with this amp and it shines for both. Sounds great, ridiculous low end is there if you want it and you will have no problem with volume!! :)

So there you have it, my 2 cents whether you wanted it or not :hbang:
 

Downrazor11

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I see this thread is pretty old but thought I would offer my experience with the B-52 AT-100. I guess I should qualify myself here. In the last 10 years, I have owned about 28 tube heads, Mesa, Marshalls, Fenders, HiWatt, Randall MTS. I play a Les Paul Custom for high gain tones (Tool, Chevelle, Deftones, Metallica, etc) and a Strat for blues (SRV, KWS).

I'm also involved in the electronics industry and love tinkering with tube amps. As such, I bought my first AT-100 for that purpose, to mod and tinker with for fun. So I will second the motion that has been made in this thread, these things are dirt cheap. Over the last 5 years that I have owned B-52s, i can not imagine having more fun on 300 bucks. I now have 3 of them, but typically have 2, my main experimental amp, and one extra. I normally try new circuits on my experimental amp and break them out on switches or pots, once I get the tone I like, I then hardire the winning circuit into the second amp.

A couple quick points or pros and cons about this amp.
Bruce Egnater designed this amp for B-52. In my opinion, he did an excellent job and from a schematic perspective, this would be my signature amp. The preamp are really where the magic happens in this amp, the power section is where the improvement can be made.

The clean channel is almost exactly a Fender twin pre. Sounds awesome. No complains. I have not done anything to the clean channel. If a mesa clean channel sounded this good, or took pedals this good, it would raise mesa's loyalty I think.

The overdrive channels are a Marshall jcm900 circuit hot rodded with an extra gain stage. But, the really great addition that makes this 10x better than my DSLs is the contour switch. Most people call this amp a poor man's mesa (recto), but in fact, the tube rectifier is the only feature even close to a mesa amp or circuit.

Pros:
1. Very inexpensive
2. Sounds great, more Marshall than a Marshall for me.
3. Very versatile. Clean, blues, metal, it sounds really good for all without a consession.
4. Tube rectifier. I like alot of sag. I'm addicted to tube rectified amps when playing high gain.
5. 3 channel. It is actually a 2 channel, and the high gain channel has two modes.
6. Exceptional clean channel.
7. Higher gain amp. Plenty of gain.
8. Sounds great with a Les Paul or a strat. This might seem like a silly thing, but it isn't. You simply can't play SRV on a Recto in stock trim.
9. Switchable effects loop that switches on the return side. This allows a ton of cool hookup options, my favorite of which is to use an offboard preamp and when you switch on the loop, you are now playing an entirely different pre over the b52 power section. Especially handy for JMP-1 or ADA MP-1 users.
Cons:
1. Heavy
2. According to some tube experts that help me out every so often, a single 5U4 Recto tube is only good for 50 watts, and the amp will roll off the bass hard trying to rectify 100 watts with only 1 tube.
3. Build quality. I think the build quality is great considering the price point. You will not gain much by replacing any components except maybe little less noise. But I do agree despite my love of this amp that it could be so much better. The power section does sound a bit anemic sometimes.

Now the good stuff. I have modified 47 circuits learning and having fun. Of that, I have reversed all but 5. The most important one of all is the addition of a presence control on the high gain channels. No matter what cab I use, both with a strat or a Les paul, this amp was bright. Very bright to my ears. So I took a preamp based (not negative feedback) presence control circuit out of a mesa schematic and it worked magic. Then, to address the green channel or channel 2 thin ness, I jumped the extra gain stage so that the 2nd and 3 channel had the same tube stages. I run channel 2 in lower gain for blues, but this mod fattened channel 2 way up.

As I said, I like alot of sag. So, I always have this in tube recto mode. I also have the resonance knob at 0 to keep the power as loose as possible, no damping. This does result in the amp having less bass. My solution is to play it through my mesa oversized cab, or an old ampeg cab I have that is oversized with swamp thanks in it. If you are playing it through a marshall cab with G12-T75s, I could see how it would be unbearable, bright with no bass.

I love these things. If you have one and want to mess around with it, here are some fun things to do.

1. I do think the power section is where all the money was saved, but I can not put my finger on what exactly an improvement could be. I have though about replacing the filter caps with "better ones", but modern electrolytic caps are not really that different. Trannies would be a good place to start, but I like trying super cheap stuff instead. Perhaps the KT tube change mentioned here would be interesting. I have a big trim pot for bias on the outside of the chassis now because I used to change tube so much. But, the point is, I know the amp can sound better because of this fun trick. Take a cable and plug into the effects send of this amp, and plug you guitar into this amp. But take the cable out of the send and plug it into the return of a different amp. This is what I do if I want to know what would happen if I had the pre from one amp with the power section of a different amp. If they both have an effects loop, it is easy to find out. Especially cool if you have different tubes in a different amp, like E34Ls, or KT88s. Anyway, when I run the effects send of the b52 into the return of my Triple Rectifier, whoa! It sounds great, awesome. Likewise, when I record, I take the signal out of the effects send out of the amp, into a cab simulator, and directly to the board. It sounds awesome. This tells me two things. 1. This amp is worth having for the preamp alone. 2. There is room for improvement in the power section.

2. If you have an EL-34 based amp, or just want to hear what your DSL would sound like over 6L6s tube rectified do the same trick. Take effects send out of your other amp, and into the return of this one. Tube rectofier on, engage the loop, sag city. When you do this, set the master to 0 and plug an impedance matching load resistor in the amp you are pulling the preamp signal from.


Hey, thanks for this!! Are there any good sources where I can find how to do some of these mods? Thanks!
 

jammindude

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Hello everyone, i love the B52-AT100 so much i just bought another one and i am selling my Marshall dsl 15h, i had no idea that the dsl was made in Vietnam, i was pissed, i thought all Marshalls were made in England, NOT!!! i have had a few people do a blindfold test and the B52 won over the Marshall 8 out of 10 times, i am happy with this b52, i dont know where else i could have bought a 1/2 stack 412 and a 100 watt tube head for 450.00, my other head is in the shop and i hope it is not going to cost much, could anyone please tell me what i might do to take care of these baby`s, i mounted a computer fan behind the 4 power tubes and have it drawing the hot air out, to keep it cool, and bought a new 12at7 for the reverb and now it is fine, this one has chinese tubes, my other has all sovtek, any positive tips would help, immature assholes can keep their comments to themselves, all my guitars are made in the east, and i would not pay for an american fender if i had the money, they shut down Guild in R.I and outsourced to asia, they bought Kaman, shut down the plant in Ct my home state, and now have most of that stuff made in asia, Fender is not a good co. in my opinion, Kaman is still open, but not making as much as they used to , now all Fender amps are made in Mexico, pretty sad,
 

myersbw

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Ha! This is such a fun thread to resurface! :) Ok...my experience. Some years back I traded a Yamaha Acoustic Stomp pedal for an AT100 that wasn't working due to fuses blown. The problem? Cracked & destroyed speaker jack and blown fuse. I called the number for parts and got Egnater in California. The guy SENT ME FOR FREE the speaker jack board!!!

The good part - that amp was made better than many comparable Marshalls today. The direct audio path is analog (chips and transistors are typically channel switching logic and reverb, etc.) The boards are thick. The amp is heavy, but solid. I would've gigged it in a minute, but I don't like large heads. I would take that amp any day over a DSL...period....and slightly mod it as need be.

I've also been inside a few Jet City amps...I'll still take the B52 over them. It is a surprisingly decent amp that, like Carvin and some VHT, etc., is well under any radar. It MIGHT be an amp that suffers from the 'capacitor plague' of years back now. But, I had no issues with the one I had. If I needed a cheap backup...I'd snag one in a second.
 

jammindude

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Ha! This is such a fun thread to resurface! :) Ok...my experience. Some years back I traded a Yamaha Acoustic Stomp pedal for an AT100 that wasn't working due to fuses blown. The problem? Cracked & destroyed speaker jack and blown fuse. I called the number for parts and got Egnater in California. The guy SENT ME FOR FREE the speaker jack board!!!

The good part - that amp was made better than many comparable Marshalls today. The direct audio path is analog (chips and transistors are typically channel switching logic and reverb, etc.) The boards are thick. The amp is heavy, but solid. I would've gigged it in a minute, but I don't like large heads. I would take that amp any day over a DSL...period....and slightly mod it as need be.

I've also been inside a few Jet City amps...I'll still take the B52 over them. It is a surprisingly decent amp that, like Carvin and some VHT, etc., is well under any radar. It MIGHT be an amp that suffers from the 'capacitor plague' of years back now. But, I had no issues with the one I had. If I needed a cheap backup...I'd snag one in a second.
do you know if i can run the b52 at100 without the reverb, it stopped working, i took it out and put it in the shell of an old head so it was not sitting on top of the power tubes , but no luck, someone told me i should check to see if it can run (safely) with verb unplugged??
 

Pete Farrington

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if it can run (safely) with verb unplugged??
If you want to do that, then I suggest to also remove the valve (12AT7) in V10 socket.
But why not try a new tank, or get a tech to do so for you?

The AT-100 I own has a tri mode rectifier switch with the options of class A, class A/B, and solid state.

I know what these mean, but when I switch to class A does it change the whole amp to class A or just the rectifier circuit?

Interesting amp! https://music-electronics-forum.com/filedata/fetch?id=812574
Regarding the ‘Tri-Mode Rectifier’ switch, from what I can tell, the 1st ‘Tube A’ mode looks like it switches in the 5AR4 rectifier and puts the output valves into shared, unbypassed cathode bias. Possibly not really class A per se, but perhaps fairly close? Once the signal level results in the class A limit being reached, it would take a lot of additional drive signal to increase anode current any further. Due to degenerative feedback at the cathode coming into play, because the signal cancellation at the cathode would momentarily cease. So the technical difference to a proper class A amp might be academic.

The second ’Tube AB’ mode looks to still use the valve rectifier but changes from cathode to fixed bias.

The 3rd ‘Solid State’ mode stays in fixed bias but changes to solid state rectification.

I also have the resonance knob at 0 to keep the power as loose as possible, no damping
Just to note that resonance at zero means the power amp damping of the speaker cab’s bass response is at its maximum, as tight as possible, the negative feedback is doing its best to keep things under control.
As the resonance control is advanced, negative feedback, and hence speaker cab damping, at the bass end of the freq band is reduced.
When resonance is at max, there’s no negative feedback and hence minimal speaker cab damping, at lower freqs. And
lotsa boomy bass!


throw in a quad of KT66's They Really wake this amp up

Perhaps the KT tube change mentioned here would be interesting
Just to note that unless there’s solid info that the PT is up to it, that wouldn’t be a good idea, as KT66 draw >40% more heater current. ie a KT66 quad requires 5.2A, compared to 3.6A for a quad of 6L6.
 
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myersbw

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It is some amp with some space. Should not be difficult to add a filament transformer (maybe use what you want for a KT66 quad and leave the original PT filament to feed the preamp-side?). I agree with Pete, just pull the V10 tube and keep the reverb pot off (to ground) and you'll be fine. I'm not a metal sort of guy, but it would create some very nice high gain tone and not too bad regarding noise.
 

jammindude

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Thank you guys for your input , the low -res sounds better fully clockwise, with celestions or jensens, i use the footswitch to keep the reverb off, just for pc of mind, lol i tried a new tank and nothing, so i got a boss 63 fender reverb pedal, these things are great, the guy i got it from did not know what he had, and i told him but he did not care and traded me for some work, one thing people mis-understand is solid state ode does not mean it is running on solid state, it just means tightness comparison, one thing i noticed is previous owner installed a bias adj, that looks like an input jack on the back, nice to not have to pull it apart to adjust,
 


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