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GA-20T with a hum


6Strings

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Hey all - I have had my GA-20T combo amp for over 30 years... this is a great amp! It has worked without fail ever since I got it. It has been used at many recording sessions over the years. I was playing it at a low volumn and the output got lower and lower and then went out completely and now it only hums. The volumn controls make no difference (0 to 10). Also, if you unplug the guitar and touch the 1/4" plug it does not have any effect... as if it was not pluggd in at all. I've had it at the Amp Doctor for over a month and he is stumped. Everything appears to be working; transformers OK, tubes OK, caps OK, speaker OK, resistors OK and there appears to be no wiring issues. All we have is a hum. I've downloaded several copies of the schematic and we have followed all the wiring which appears to be correct and unchanged. Does anyone have any ideas? Any help would be greatly appreciated. I will be going into the studio to work on our new CD and wanted to use this amp... it has a fantastic tremelo. Thanks and Cheers!

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Sinse everything checks out ok, and it still does not work, I'm going to guess something was missed. Meaning something that was checked and thought to be ok isn't.

 

I am going to guess it is a tube, problably the preamp. When a pre tube goes it can behave exactly like that, and sometimes "testing" tubes doesn't catch it.

 

Of corse, I'm guessing for fun to see if I am right, but truly I would try REPLACING the tubes to confirm the are all good.

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