Bad hum on SS amp, is it tied to reverb tank?

[noahcopeland]

Hiya,

Bout to play a gig tomorrow night with an old Tech 21 Trademark 60. Haven't gigged like this in a long time.

To my disappointment, my amp's got some bad hum, like 60 cycle type hum. It's there even without the guitar plugged in. I'm trying to see if there's anything I can do last minute before tomorrow's gig.

I noticed that when turning up the reverb knob, the hum gets WAAAAy loud. I'm thinking the verb has something to do with it?

So I disconnected the RCA jacks to the reverb tank. Same issue.

I found the other ends of the RCA cables that were connected to the mainboard. Disconnected them too. SAME issue.

Any ideas? Perhaps it's not tied to the reverb at all?

[The Dude]

If it's been sitting for a while, my first suspect would be dried out electrolytics, but it could be a number of things- solder joints, DC on the output, etc., etc. I'd start by checking power supplies for ripple. My experience is that you'll never get a schematic from Tech 21, so you'd have to figure out the supply points on your own. If you're not an experienced tech, this could be a bit difficult. The only quick check you might do is hook a short cable from effects send to return to eliminate the possibility of a bad cutout jack.

[glebert]

Reverb may add hum to the signal chain, but if you turn the reverb down all the way and the hum is still there it is unlikely just a reverb problem. Do you have the footswitch? I think the reverb is switchable on this amp. Unfortunately Tech 21 will not give out schematics, but if you call them and ask for tech support you will probably end up talking to the guy who designed it. At least that is what happened to me when I worked on a TM60. Nice guy, I think his name was John.

Probably not something you are going to fix by tomorrow night unless it is dirty effects loop jacks as The Dude mentioned.

[g1]

Also, any fault related to poor reverb jack connections will not be shown by leaving the cables disconnected. Try reconnecting them and twisting them back and forth a bit to clean up any oxidization.