B52 Low Volume

[bikeonthebrain]

Hello everyone, this is my first post and I am not what you would call "experieced" in the amp fixing world, but I'm eager to learn and I have some experience with various electronics.

So, I have a B52 AT 100. A month or so ago the amp started to make crackling noise (sounded like a bad cable, but wasn't). I tool it to the local repair shop and they replaced 2 preamp tubes, which seemed to fix the problem for about 1 week. Then while playing at a fairly low volume the amp suddenly made a very loud hissing noise and the volume level dropped to where it was bearly audible. If I turn the volume to about to 3/4 of the way up you can hear it very faintly, the clean channel is also slightly distorted. Since then on the recommendation of the repair shop I replaced all of the tubes (pre, power, and recto), I have tried different cabs, guitars, and cables.....it still doesn't work.

I opened it up last night and looked for anything burnt, broken, etc...I thought I had found a burnt resistor next to the speaker out jack. I replaced it and still nothing.

So I am trying to troubleshoot this thing on my own since I have dropped $200 on tubes all ready and don't want to bring it in to the shop before I try my best to diagnose....the amp isn't worth that much! Please if you have any suggestions as to what to look for, at, test, anything please let me know.

Thanks,

Eric

[Mars Amp Repair]

Could you tell if the 'hissing' noise come out of the amp or the speakers? If it came out of the amp, that could have been the resistor burning up...did you smell anything?

You say you think the resistor near the speaker jack was burned, but was it? It could have been burned but something else caused it to burn that is now itself 'burned out'. It could be a clue if you knew what reference number or value the resistor was.

Let us know if you can read the reference number where the resistor came from & or its value. This kind of issue could be many things, but you really need to have some test equipment & some knowlege of troubleshooting to go much further.

glen

[bikeonthebrain]

I'm not sure if it came out of the amp or speaker, it happened so fast I wasn't really paying attention to that.

The resistor was R103 (47ohlm). It was definately burned up, but like you said it could have been anything that caused it before the output. I have heard that these amps are notorious for having bad output trannys, would a bad tranny cause something like that?

[Andy]

would a bad tranny cause something like that?

Low output and distorted sound are two very common effects of a bad OT. a friend of mine had one of these, and his OT went bad after a few months. it was still under warranty, so he just took it in and they replaced it free of charge.

[drewl]

First of all, if you had it fixed and it died after a week? I'd take it back to the "repair shop"
They had you replace all the tubes in it?
I've worked on a couple and they have several pc boards with ribbon cables between them. make sure all of those are connected properly and didn't come loose.
I know B52 has a fan kit they suggest you have installed to keep the rectifier tube and power supply board from overheating.

You can isolate the problem to pre amp or power amp by seeing if you have signal from the preamp at the fx loop output, and try running a signal into the fx loop return to see if the power amp section is working.