Ampeg B-100 (solid state)

[saulecker]

I just picked up an Ampeg b-100 bass amp, circa 1976 or so. I purchased it with a known problem: It sounds like it has a distortion pedal plugged into it. According to the guy I bought it from it's NOT a speaker problem. He says he tried 2 other speakers and had the same results. I believe him as the first thing I did when I got the amp home was pull it apart and I could see that the speaker had been removed. Also the speaker wasn't hooked up as he'd been trying others. Unfortunately, I don't have another speaker to test it out. While I had everything pulled out I did a visual inspection of the board to see if there were any obvious things wrong. Everything looked ok and there were no obviously blown capacitors or goo or anything on the board. I then hooked it up and it played it for the first time. It really sounds like I've got an overdrive pedal plugged into it.

So my question: Other than a blown speaker, what could cause this?

Thanks in advance for the advice.

[saulecker]

After some google and some reading I'm convinced that one or more of the caps is the cause of my problem. Is there a good place to buy replacement caps?

thanks

[imbuedblue]

Try http://www.mouser.com

[Rob Mercure]

Actually that's a classic sign of blown output or driver transistors - how's the power output? But SS filters dry up just like hollow state - do you have a hum problem? If not I suspect the transistors but Enzo'll probably add his wisdom to this and straighten you out.

Rob

[Enzo]

Don't assume the speaker is OK, find out. You may not have another speaker to try with the amp, but do you have another amp you could connect to those speakers? Even a stereo system.

And the amp itself? I might think open output transistor, but not shorted. Certasinly check the output stage power rails. Are they both up to the same DC and free of ripple? How about the low voltage rails for the preamp? Same questions.

[saulecker]

There is no hum. Amp is really quiet.

Actually, the more I read about this the more I think I might be out of my depth. I can solder, but as soon as I read "output stage power rails" I thought "ok, maybe I should take it to that nice place with the good reputation by my work". thanks for the advice and maybe I'll start reading up on electronics. I've always been interested, but never motivated.

[saulecker]

I might think open output transistor, but not shorted.

Just a quick followup:

The place I took it to (Bull City Sound in Durham, NC) said "It ended up being your output transistor. It seems it was stuck open." I hadn't told him anything that you guys had said because I wanted to see what he would come up with. He also said it was an unusual problem, so super props to Enzo!!

[ryan3738]

B-100

Do you remember how much you paid to have the amp repaired?