Gibson GA-20 Minuteman Problems: All buzz, no signal!

[Sean Sullivan]

My friend has a Gibson GA-20 Minuteman amplifier that recently stopped working. When turned on, it just buzzed and won't pass signal. To me, that sounds like a bad transformer, and the amplifier used a phase-inverting transformer instead of a tube, and they are know to go bad. Here's the schematic:

http://www.informatik.uni-bremen.de/~da ... a20rvt.jpg

[Boogdish]

Buzzing and not passing signal is not necessarily a busted transformer, it could be a bad ground, a shorted grid input, plenty of things.

1.Try different tubes
2.Open it up and make sure everything looks like it's connected the way it should be, look for shorts, look for burnt resistors, look for things that might have exploded.
3.Find a schematic for the amp and check the voltages on the tubes and compare to the voltages printed on the schematics. Be careful not to electrocute yourself.
4.Check for connectivity across the jacks/pots/sockets and other electromechanical parts. These take the most wear and tear and are most likely to fail.

If you still can't figure it out after all of this, I would still take it to somone that fixes these things on a regular basis and have them look at it before replacing the transformer, unless you've got a line on a really cheap one.

[suppositron]

Buzzing and not passing signal is not necessarily a busted transformer, it could be a bad ground, a shorted grid input, plenty of things.

1.Try different tubes
2.Open it up and make sure everything looks like it's connected the way it should be, look for shorts, look for burnt resistors, look for things that might have exploded.
3.Find a schematic for the amp and check the voltages on the tubes and compare to the voltages printed on the schematics. Be careful not to electrocute yourself.
4.Check for connectivity across the jacks/pots/sockets and other electromechanical parts. These take the most wear and tear and are most likely to fail.

If you still can't figure it out after all of this, I would still take it to somone that fixes these things on a regular basis and have them look at it before replacing the transformer, unless you've got a line on a really cheap one.

All of those things. I'd say it would be way more likely that his input jack or a tube went bad than a transformer. If you have a signal generator you could try injecting signal at various stages.