Bathtub Reverb - Issues

[SamuelG]

This is how I would add a deep switch, that way I could have it original or deep tone if I wanted to.
I would not mount C2 on the PCB, I would run 2 wires from the PCB holes for C2 to a DPDT switch and then mount the capacitors on the switch.
It would be a lot easier to change the caps on the switch if you want to keep trying different values.

There is a way to use a DPDT ON-ON-ON switch so you can have 3 different settings if you wanted Normal-Deep-Bass settings which I have used in the past, It gave me normal for guitar, deep for a deeper tone on guitar and Bass for Bass guitar.
If you would like to see it let me know, I would have to find it on my computer, I'm to tired now at 3.30am to look for it.
Cheers
Mick

EDIT: I couldn't help myself so I drew the 3 way switching circuit up in KiCad just to show everyone, I have been meaning to start a new thread just for mods and when I do I will place all this in there as well.

I was thinking about this mod for C2 in the Bathtub Reverb. C2 also isolates the Reverb module from the high plate voltage. Doesn't that mean all the mod caps should be rated for over 250V DC?

 

[SamuelG]

A suggested list available from Tayda

C1	470nF 630V	A-4849
C2	4u7F 400V	A-3338
C3	22uF 400V	A-3336

 

[Tassieviking]

If I did it on a HV capacitor I think I would add a resistor (2M-5M) to each extra cap to pre-charge it up to HV, I don't think the resistor will change anything tone wise but will help with pops and arching in the switch.
The caps would have to be HV caps just like they are paralleling.
I don't think you would need that much more capacitance, I would try with 22nF original, another 22nF for deep and a 100nF for bass.
I think it's try and see unless someone can run a sim on the circuit.

Coupling caps are not usually very big in valve amps, usually somewhere between 22nF to 100nF is very common.
https://www.ampbooks.com/mobile/amplifier-calculators/coupling-capacitor/