B-52 AT100 Schematic

[rf7]

Does anyone have a schematic for one of these amps? B-52 is not getting back to me at all.

[Enzo]

Really? Last time I contacted B-52, they had the schematics I wanted to me the next day, along with troubleshooting suggestions, and they even followed up on me.

meanwhile i do have that one.

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

[drewl]

Figures, I've fixed two of these and now a schem pops up.....
Thanks again E, I'm ready for the next one!

[rf7]

Thanks Enzo! I emailed them and left a phone message, but got no response.

[tonal_idiot]

Thanks for the schematic post. My son's distortion channel died this evening. The clean channel is ok apparently but nothing from the distortion channel. Hopefully with the help of the schematic I'll be able to figure it out tomorrow. Thanks again!

[dtaw]

Originally Posted by drewl

Figures, I've fixed two of these and now a schem pops up.....
Thanks again E, I'm ready for the next one!

What kind of problems did you run into on these amps?

I was looking at the schematic, because someone in my area wanted to replace the power tubes and I was thinking with a 1K bias trim pot there is hardly any room for adjustment on this amp, or am I missing something?

[heavyrocks]

Enzo, major thanks, I've been looking for this all week.


The problems this amp has given me over the past two years:

Power supply burn out
Handle ripped off top
Reverb - when new, sounded weak (when turned to 10 sounded like it should be at 2), recently cut out all together

Make no mistake, this it a $700 head. Good for the price, but I would save up and get a Mesa if it got stolen/lost/broken beyond repair

[Psopho]

Does anyone know the specs for the power transformer? I have one with a blown power transformer and apparently I'm looking at about $800NZ to replace it!

[heavyrocks]

$800 for the transformer? I paid $800 for the whole head.

[Enzo]

Do you live in New Zealand though?

[heavyrocks]

ahh yes, that would make a difference, wouldn't it

[Psopho]

Yip, that's $800 New Zealand Dollars. Currently equates to $450US and 350Euro

[heavyrocks]

Ehh, that still aint cheap. That heads been nothing but trouble for me, it just started getting really quiet on me a week ago. Something in the power supply section but I haven't narrowed it down yet.

[Amp Kat]

One of the best sounding amps out there but they are just a pain to keep going. One of the problems is the connectors or not good at making contact and open up during playing. Look at those real good especially the speaker jack.

[heavyrocks]

no doubt, the tone's delicious, the construction is where all the cost-cutting happened

[heavyrocks]

Nah, I don't think it's a broken connection. I think something must be burnt out. The signal is there, and the tone isn't messed up, it's just super-quiet. I have a 8W practice amp that's louder than it is now. I figure it's something in the power section, but beyond that I'm kinda stumped. I know it's not the power tubes, cause I tried just playing with the first pair, and then just playing with the second pair and there was no volume change. All the tubes, (power, pre, rectifier, and reverb) glow and none of them make any noise when tapped with a pencil. Do you know how one would check the rectifier tube? I've heard that can be a possibility with volume drop.

[heavyrocks]

Also, there was no burnt smell or obviously singed components.

[Enzo]

Why have you decided it is in the power amp or power supply? If the preamp signal simply doesn;t get to the power amp, it will also sound very weak.

If a broken connection opens the signal path, in most guitar amps ther is enough crosstalk that something still comes out just from coupling.

That is why the first thing we usually suggest in a dim amp is to patch from send to return in the FX loop jacks, and also at the preamp out and power amp in jacks, if the amp has them.

Certainly a broken connection at a coupling cap can seriously reduce signal level if between stages. (Well, I suppose if it is a coupling cap it has to be between stages.)

[heavyrocks]

Enzo, thanks. I patched the effects send directly to the return and the volume came back. Any tips on commonly broken connections to look for?

[Enzo]

Your return jack has bad contacts. The little contacts on the jack that open when something is plugged in. If they get dirty or oxidized, then when nothing is plugged in, they don;t complete the electrical circuit like they should.

Clean those contacts or replace the return jack.

[heavyrocks]

I'm a little confused.

It's not back 100%, maybe like 50%. Also before when it was working fine, if I switched on the effects loop there was always a slight signal drop, nothing too significant though, a much smaller drop than I have now.

For a rough comparison, yesterday when my signal was all the way down, I could crank it at 6AM and my upstairs neighbor would never hear it. Now with the effects send patched to return its about loud enough to play with a drummer when cranked. Usually when playing with a band I only have the master vol between 12 and 3 oclock.

[Enzo]

OK< then you have more than one problem. Fix the FX loop, and move on the the rest of it.

[heavyrocks]

Yeah, I figured that wasn't right, but the FX loop was like that since I got it. Any pointers of where to start?

[Amp Kat]

There was a tech in Cali that reported he had to redue all of those white connectors as they were not making good contact. Not sure which connectors he used or if he just soldered them into the board but he said there were more than 2 causing problems so keep that in mind.

[heavyrocks]

Yeah I bet, those things feel cheap as hell. I don't know why they couldn't use one ribbon cable like Mesa. Arg!

[heavyrocks]

I'm contemplating lining the back grate with pancake fans so the damn thing will stop overheating and dying on me.

[showme]

Okay, someone please tell me if I'm absolutely making a mistake.

I went to guitar center yesterday and played a used B52 AT 212 @ $400.00and absolutely loved the sounds I was hearing. Everything seemed to work fine so I put it on lay away.

I've read a substantial amount of bad reviews prior to my amp decision but, what can I say, I like the way it sounds.

I'm trying to convince myself that it's worth the trouble, but maybe one of you that knows first hand can talk some sense into me...

[showme]

Okay, someone please tell me if I'm absolutely making a mistake.

I went to guitar center yesterday and played a used B52 AT 212 @ $400.00and absolutely loved the sounds I was hearing. Everything seemed to work fine so I put it on lay away.

I've read a substantial amount of bad reviews prior to my amp decision but, what can I say, I like the way it sounds.

I'm trying to convince myself that it's worth the trouble, but maybe one of you that knows first hand can talk some sense into me...

[Enzo]

Yes, you obviously made a mistake. You posted the same thing twice in a row. That looks like a mistake to me.

or is that not what you meant?


You should buy an amplifier that sounds good TO YOU. It doesn't matter in the slightest whether I like the sound of it, it won;t be my amp.

Guys write reviews all the time. "This amp sucks." Well, what does that mean? He didn;t like it for some reason or other. Maybe he was expecting metal tones from a Fender Deluxe. Maybe he wanted smooth jazz tones and he bought a 5150. Who knows. if a guy like me who fixes amps for a living tells you that they all break a lot, then don't buy it. But when a guy hates the tone, that is subjective. if you like it, then it sounds good to the guy who cares - you.

[heavyrocks]

I second Enzo. The B-52 AT series has good tone if that's the tone you're looking for. But treat it more gently then you would an infant. Definately, DEFINATELY!!!! buy a clip on fan and attach it to the back to keep it cool. THEY GET HOTTT!!!!! I've replaced a power transformer and several tube sockets just from simple overheating. Also be careful of the handle, mine pulled out of the wood. But tone-wise, it's a great bargain.

[tekhed7]

Well... I just finished Fixing 1 of these sorry behemoths.
Sure enough, contacts at the input jacks & impedence selector slide switch were both crapped, but the real problem with this combo was that a hot-running, common cathode resistor for the power stage... that white, 15 watt 110-ohm power resistor on the power supply board, had cracked free of the foil on one end.
The young guitarist had changed All the tubes with 'GT' tubes in an effort to "combat" the resultant major power drop (to almost nothing) when the resistor post went "open". Silly boy.
After I got the input jack board repaired for a busted HI jack, and the Line Out jack remounted back up on the rear panel with a new "front-nut", I went probing & found that loose power R. R95 I believe.
After the head was all spiffed up, the cab rewarded me by having it's entire front (dual 12") speaker panel simply flop out of the cabinet! They freagin' STAPLE those front speaker panels in!
Ahhh, well. A bit of wood glue & thin screws & she's solid.
Customer was told by "everyone" that his power drop was all probably a bias issue! (??)
Never ceases to amaze me the lack of understanding that musicians can have of their equipment. And it seems there's lotsa people to chime in with their 2 cents worth. (More than what that advice was worth)
BUT... that's what keeps us techies in business, Huh?

[glsharum]

I got one of these beasts with a bad power supply. I got it at a good price and did not want to put much into it. So I replaced the PS with after market ps to run the plates and heaters. I got a small low voltage supply from hammond to power the 12 volt needs. I then removed the bias selector switch, which was a disaster, removed the tube rectifier (I like SS), and disconnected the bias circuit. I put marshall type of bias circuit on a small board power by PS bias tap. I am getting ready to put it back together. At least the bias circuit will be more reliable. I think the stock system is what killed the PS to start with.