Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jonas on April 05, 2026, 03:55:03 pm
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Hello, I have a Gibson Scout (GA-17RVT) on the bench. The amp works but has some hum, loud popping, sizzle sound at note decay when played hard and some reverb feedback.
Other than a few earlier repairs, the amp looks to be mostly stock to match the attached schematic. Transformers are original. Would you recommend any of the below modifications as an improvement?
1) remove this component / replacing with .001 or .002 (not really a question....)
2) Add screen grid resistors and (or) grid stoppers?
3) The reverb pot is directly connected to the volume pot. Would a switch here (ground reverb input grid and separate connection between both pots) be a good idea? The reverb is off with the foot switch but you could still I'm thinking a switch pot for the reverb would make sense.
4) One leg of the heater supply is grounded. Rewire heater supply with artificial ground
5) Three prong cord already added.
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6) Are there any grounding scheme changes that are typically recommended with Gibson amps?
7) slow down the tremolo speed
I will do voltage checks, etc. I anticipate some caps to be leaking
Thanks!!!!
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Normally, a good start is cleaning all the pots and connections, and replacing electrolytic and paper capacitors that are past their prime. Check resistor values, etc. At that point, you know you have a good foundation.
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What does the customer want? No pops or sizzles? If that's the case, then don't mod it, just fix it:
-Clean all pots, jacks, switches and sockets-test tubes, replace as needed,-noises persist? check for leaky coupling caps, filter caps not filtering, bad solder joints, noisy resistors, noisy but functional tubes, etc...general trouble shooting.-check DC voltages for large discrepancies from "normal" or what is stated on schematic-confirm proper power output using standard methods
The Sprague filter network component (#1) can be replaced with a wire if your schematic is accurate... AND if the customer wants that. I recently repaired an early 60s Gibson amp where the circuit in the amp did not match any of the schematics I could find for it. Looks like you've already confirmed that yours match?