Anybody know anything about the B-52 AT line of amps?

[mrmcsick]

I picked up a B-52 AT-212 the other day and Im pretty happy with the sound, just acouple complaints though. It makes way too much hiss noise when cranked up. Clean channel can only be turned up alittle more than halfway before its starts to get alittle dirty.

It has way too much gain for me, I have it turned up to around half way. This is whats in it. 1 5ar4 rect. 4 6l6's. 4 12ax7's for preamp. 1 phase splitter. 1 reverb and 1 effects loop. Now since it has more gain than I need can I just replace some of the 12ax7's with y7's to cut it back and even get rid of some of the hiss and maybe get more headroom on the clean or is the dirty clean related to power tube overdrive and not the preamp?

Anyone have a schematic or know of any mods for these amps?

[rockon1]

I picked up a B-52 AT-212 the other day and Im pretty happy with the sound, just acouple complaints though. It makes way too much hiss noise when cranked up. Clean channel can only be turned up alittle more than halfway before its starts to get alittle dirty.

It has way too much gain for me, I have it turned up to around half way. This is whats in it. 1 5ar4 rect. 4 6l6's. 4 12ax7's for preamp. 1 phase splitter. 1 reverb and 1 effects loop. Now since it has more gain than I need can I just replace some of the 12ax7's with y7's to cut it back and even get rid of some of the hiss and maybe get more headroom on the clean or is the dirty clean related to power tube overdrive and not the preamp?

Anyone have a schematic or know of any mods for these amps?

Yes you can try tube substitutions but I always find a 12AX7 works better in a 12AX7 circuit than a sub tonally. 5751's might be a better bet with thier closer specs. Of coarse you could just keep the gain down low.
Have you tried simple stuff first like plugging into the low input? bob

[mrmcsick]

Yeah I tried the low input but there is no reason to go more than half gain and I play death metal and we love gain.

Looked and saw it has Sovtek 5881WXT power tubes. the first 3 preamps are Electro Harmonic 12AX7 EH tubes. The rest of the preamps are china no name 12AX7's with 1 12AT7 in the middle somewhere. Im guessing the 3 Eh's are actual preamp but the manual says it has 4 preamp tubes. Why would they throw a no name china in with the EH's? Should I try and upgarde all the china tubes?

[Mark Black]

Here http://music-electronics-forum.com/s...ead.php?t=9765 you will find where Enzo has kindly posted the schematic (in color no less).

Those amps are designed for big-bottom high-gain Boogie-ish stuff, although the clean channel is usually pretty clean. With high-gain usually goes high-hiss...

The stock speakers may not have the best sensitivity - try it jacked into a 4x12 Marshall cab if you have access. For that matter are both the internal speakers working?

Also make sure you are using the SS recto setting for best clean headroom - the other two settings are progressively more squishy.

Beyond that there is always the possibility the amp has a problem, perhaps as simple as worn power tubes or improper bias. The amp was designed around 5881's - if somebody just slapped some 6L6's in there things could be off.

[mrmcsick]

Ok my bad. I just assumed it had 6l6's since that is what the litterature states. Yeah I plug into the low input. I play alot of stuff all the way up to death metal and those people love gain but there is just too much in this amp. I never go past 12 oclock.

Check out the tubes and heres what they are

Tube order across the chassis is V1-2-3-4-10-11-5 then the power tubes and recto, V6-8-7-9-12

V1-3 Electro Harmonix 12AX7 EH
V4,11,5 No name China 12AX7B
V10 No name china 12AT7

V6-9 Sovtek 5881WXT
V12 Electron Tube China 5AR4

ok so 1-4 are preamp 10 is reverb 11 is effects loop and 5 is the phase splitter Right?

[rockon1]

FWIW- The sovtek 5881's arent 5881's and really arent 6L6's but closer to 6L6's than 5881's. You could try a couple 5751's in the first to spots or even the 12AY7 as you mentioned. Bob

[mrmcsick]

Does the phase splitter even affect the sound? Can someone please help me understand what is happening in the different selection of the rectifier, tube A, tube A/B and Solid state?

[rockon1]

Does the phase splitter even affect the sound? Can someone please help me understand what is happening in the different selection of the rectifier, tube A, tube A/B and Solid state?

Some would say the PI doesnt affect tone much if at all. I find differently. I actually like to find a PI that sounds best first then do some tube rolling in the other spots.

Tube rectifiers give more "sag" as they try to keep up with power demands at higher volumes (from my minimal understanding). Some players attribute this sag to note "bloom". SS will give the least sag and stronger punchier sound. Always prefered SS rectification myself. Not sure what the difference on your amp is between tube A and tube A/B rectification. Bob

[Mark Black]

"Solid State": Power tubes fixed bias, using solid state rectifier diodes for B+. Most headroom & punch.

"Tube A/B": Power tubes fixed bias, using tube rectifier for B+. Bias voltage is scaled to accommodate the lower B+ voltage. Much like the Solid State setting but more sag, less punchy.

"Tube A": Power tubes cathode-bias, using tube rectifier for B+. Earliest breakup and most sag. Runs the power tubes pretty hot at idle, may not be the best setting to leave it in if the amp will be idling for long periods of time.

[Robmosis]

Off the subject a little

I know this is off the subject a little but, I have the AT-100 also and have changed the tubes out(which is a must to let this amp really shine) and it sounds fantastic. My only problem is that 100 watts is to loud. I don't want to shell out hundreds of dollars for a hot plate so I was wondering if a wattage switch could be installed on it so that you could select between like 25 50 and 100 watts? I have taken a power tube out of each side and it works to cut it down. Is this a safe thing for the amp. I have been doing it for a while and haven't had a problem yet but I would like a little more control of my output.
Thanks
Robmosis

[rockon1]

I know this is off the subject a little but, I have the AT-100 also and have changed the tubes out(which is a must to let this amp really shine) and it sounds fantastic. My only problem is that 100 watts is to loud. I don't want to shell out hundreds of dollars for a hot plate so I was wondering if a wattage switch could be installed on it so that you could select between like 25 50 and 100 watts? I have taken a power tube out of each side and it works to cut it down. Is this a safe thing for the amp. I have been doing it for a while and haven't had a problem yet but I would like a little more control of my output.
Thanks
Robmosis

Its safe. To be even safer set the amp to 1/2 the cabs impedance. For example-if your using an 8 ohm cab set the amp for 4 ohms. Bob

[mrmcsick]

Rob, what tubes did you throw in?

[Robmosis]

Thanks for the responses. I will adjust my ohms to match like you said Bob. Also I replaced the power tubes with Electro Harmonics and the pre amps with JJ's. The amp sounded good with the stock tubes. (I bought one when they first came out and they at least used matching tubes in them then. I have heard people say that they have been throwing in just any tubes at the factory.) Either way, when I swapped to better ones the amp just came alive. I have played many great tube amps and this one truly suprised me with the sound that comes out of it. You can pretty much get the sound your looking for with a little tweaking.

[Robmosis]

another Question

Just another question about my AT-100 head. In the order of the preamp tubes across the chassis why do the 1st and 2nd preamp tubes have a metal housing around them and the other tubes don't? I am new to tube amps but I want to learn as much as possible about how they work. I want to be able to fix, mod, and build one myself in the future. I know the dangers so I want to understand everything before I dig in to one. If anyone could give me an answer to the preamp question I would be greatful.
Thanks Rob

[Enzo]

Shields are used more on the first stages of an amp because they are the tubes using the most gain on low level signals. The stage boosts the signal but also the noise. By keeping the noise flooor as low as possible, it keeps noise out of the amp.