Are you certain that it's C1 that 100n/.1uF? From zooming in on the image of your board it looks unpopulated, and maybe that .1uF is some other cap.
R1/C1 are an RF filter. Unlike most amps, there is no series input grid resistor on the first tube stage, your signal goes directly to the grid of the tube. This gives Radio Frequencies/stations a real chance at being involved in your gig/practice, but seems rare? Thought I've had other amps with RF issues and it's quite annoying.
It seems many V-series amps don't seem to have any R1/C1 (Channel 1) or R7/C4 (Channel 2) [hangman/Steve could probably offer info on how rarely he sees them fitted].
I think R1/R7 are good in practice/theory (and a little larger isn't an awful ideal), but the input resistors to ground (R2/R8) are absolutely enormous, probably beyond spec for most amps. though in realtime, whatever guitar or piece of gear right before your amp's input is probably running in parallel so the tube is probably not actually seeing 5.6M to ground but less...
Anyhow, 1k and a small value cap for one of the channels might bail you out of situations you could theoretically get in where you are sending such a low output impedance signal to the amp and/or in a such a RF prone area (ever play near a college radio station?!) that you get RF at the input grid of the amp and it's broadcasting through your amp(!).
If you add a resistor and/or cap on even just one of the two channels here, you might save yourself from the headache of that (albiet unlikely) situation ever occuring, or having a plan B if it does. I added either an R1 or R7 resistor and no cap myself, but can't remember which one.
Just be sure you look close and make sure the input wire is properly located if you do this, because obviously the input signal is routed to the tube side of the resistor if it's not there, unless there is a jumper in place of R1/R7....
R1/C1 are an RF filter. Unlike most amps, there is no series input grid resistor on the first tube stage, your signal goes directly to the grid of the tube. This gives Radio Frequencies/stations a real chance at being involved in your gig/practice, but seems rare? Thought I've had other amps with RF issues and it's quite annoying.
It seems many V-series amps don't seem to have any R1/C1 (Channel 1) or R7/C4 (Channel 2) [hangman/Steve could probably offer info on how rarely he sees them fitted].
I think R1/R7 are good in practice/theory (and a little larger isn't an awful ideal), but the input resistors to ground (R2/R8) are absolutely enormous, probably beyond spec for most amps. though in realtime, whatever guitar or piece of gear right before your amp's input is probably running in parallel so the tube is probably not actually seeing 5.6M to ground but less...
Anyhow, 1k and a small value cap for one of the channels might bail you out of situations you could theoretically get in where you are sending such a low output impedance signal to the amp and/or in a such a RF prone area (ever play near a college radio station?!) that you get RF at the input grid of the amp and it's broadcasting through your amp(!).
If you add a resistor and/or cap on even just one of the two channels here, you might save yourself from the headache of that (albiet unlikely) situation ever occuring, or having a plan B if it does. I added either an R1 or R7 resistor and no cap myself, but can't remember which one.
Just be sure you look close and make sure the input wire is properly located if you do this, because obviously the input signal is routed to the tube side of the resistor if it's not there, unless there is a jumper in place of R1/R7....