Grid Resistors on 6G6B Bassman

[JammyDodger]

Hey All,

I have recently acquired a '63 Bassman with a 6G6B circuit. The amp is 90% original but for a couple of mods. One that I am wondering about is that there are 1.5k Resistors hanging off of pin 5 of the power tubes. I think these are called grid resistors. These are not original to the circuit. Is this just to 'tame' the amp i.e. protect it from oscillations? What is the risk if I remove them?

Thanks, Mike

[phsyconoodler]

Leave them alone.Some bassman's don't oscillate and other's do.There is no change in tone with small value resistors as grid stopper's.
When you get 100k or more there is some change in tone.

[tlpruitt]

I have a 6G6B and it has 1.5k grid resistors on the output tubes and they are stock.

[Tonic Amps]

A 100K grid resistor is pretty extreme for output tubes and mostly only found on high gain amps to keep them stable. Most amps will have 10K or less on the output tube grids. It helps curb oscillations as you are rolling off high frequencies as you raise the resistor value. To me, there is also marked change in tone between say 1.5K, 4.7K, and 8.2K, holding everything else the same. Whether that is preventing blocking distortion or just rolling off some high end, well, that depends on the amp.

You could probably remove the grid stoppers, but I'm sure they were put in for a reason. If it helps the tone or prevents oscillations, then leave them in. You could try it with the resistors out of the circuit by using a short clip lead to bypass the resistors on each tube. Then if it's unstable or the tone becomes "brittle", just take the clip leads out and leave it be.