Veering off a little, but DO THIS.................
Take the two red HV wires off of your function switch and put them on the normally open lugs of a good relay. Where the red HV wires used to be on the function switch, run some low voltage AC (or whatever you can steal from an adjacent component....I think I tapped some filament AC from the speech amp tube) to be switched with the function switch, and then to the coil of the relay. That will take away the HV sparking from your function switch. The HV inrush into the big elect. caps produce a terrible spark that pits and corrodes your function switch contacts, which will cause it to fail.
So to summarize.... Take red HV wires off of the function switch, and solder them to some normally open contacts of a good relay
Tap some 6 VAC filament voltage from the adjacent tube and run it to one of the now open lugs on the function switch
Run a wire from the other open function switch lug to the relay coil (make sure the relay coil voltage and type match what you're sending to it...eg. 6 VAC).
Ground the other side of the relay coil.
Simple, and just moves the sparking to the relay, but it will save your function switch. Those are really hard to find, and a miserable job to change out.
I have read of this mod, I will do it!! You explain it so simply that even I am unlikely to screw it up. Now to find a 6VAC relay that can handle the 300 or so volts (Rat Shack, here I come!).