Back in November, I built up the Little Gem audio amplifier, and toyed around with it for a little while before I listed it on Craigslist to see if I could make a few bucks on it. Before it sold, somebody in my area saw the ad and contacted me to see if I'd be interested in a Peavey amp head that stopped working. He couldn't get it to work, and after replacing a fuse in it, he said it "started smoking," so he didn't want to mess with it anymore. I took it, figuring that at best, I'd be able to fix it and sell it, and at worst, I'd have a bunch of nice knobs and components that I could scavenge and use for future projects.
Not wasting any time, I plugged in to see what would happen. No smoke. Good. Next, I tried the pre-amp line to see if the unit was sending any signal at all to another amp, and sure enough, the pre-amp side of the unit successfully shaped the signal, which meant that I had reverb, equalizer, and a couple other miscellaneous features.
Curious about why the power-amp side of the amp head didn't work, I cracked the case open and found this:
At the center of that wasteland stands three prongs that used to be a transistor (possibly the power transistor), and all around it were burnt out resistors.
Since the pre-amp side works, the amp-head isn't just a boat anchor. It's kind of useful, and it actually sounds better than my fully-functioning amp.
Given the disaster that is the circuit board, what's the general opinion here? Should I try to replace everything that's been burned out, and try to trace down the short that caused the problem in the first place? Or should I just scavenge the thing for parts?
This looks kinda similar to an amp that my friend scavenged. When they blow, they BLOW. You will probably find that the transistor that has exploded is one of the driver transistors for the output stage, and one or several of those output transistors will be stone dead.
TheMG said:
Yeah -- the place where the transistor used to be is just three bare wires. The transistor literally vaporized.
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