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GA55-RVT tube DC volts troubleshooting chart


wosinek

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Gibson Guitar Amplifier RANGER GA-55 RVT DC Volts Chart

All controls set to minimum, no input, reverb tank connected, 8 ohms speaker attached.

Some Hum but amps works fine except for slight squeal maybe from Tremolo bad tube.

Also, seems the DC voltages about 11% higher than schematic..today’s higher AC wall 120v ??

V1,2,4,5 - 6EU7 V3 - 12AU7 V6 - 6FQ7 V7-8 - 6L6GC V9 - OA2

 

See attached PDF DC Volts troubleshooting chart

 

Any help or suggestions welcomed.

 

Ken in Texas

Gibson Ranger GA55 RVT DC volts chart.pdf

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Hey Ken -

 

The voltages don't seem that far out of line. The schematic shows a 117V line voltage and your supply might be as much as 125V, so that's about 7% difference. That would account for most of the voltage increase you're seeing. Also, some of the resistors could have drifted to a higher resistance over time, which could cause some higher voltages, maybe as much as 5 to 10%. That's not unusual. So what you're seeing could be pretty normal.

 

As far as the squealing goes, that could very well be a tube. Get some known good tubes and start switching them out and see if you find the problem.

 

I'm not sure whether that amp has a two prong plug or three, but you might want to change it to a three prong plug if it's not. If you do that, it might also need to have the fuse holder(s) rewired.

 

Good luck!! If you can't fix it, bring it over and I'll play... I mean fix... it for you. [laugh]

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