5F1 Champ Mods - component ratings?

[mcgruff]

Hi

I'm planning to do a few mods to my 5F1 champ:

- NFB on/off switch

x1 SPDT (rating?)

- Princeton tone control plus switch to remove it completely from the circuit

x1 1M log pot (rating?)
x1 4.7nF capacitor Orange Drop (rating?)
x1 470pF capacitor silver mica (rating?)
x1 22uf capacitor electrolytic (25V - OK got that one)

- cathode resistor bypass, both gain stages, on/off/on will provide two cap options plus normal, unbypassed option

x2 on/off/on switches (rating?)
x2 wideband caps, 22uF (25V)
x2 treble boost caps, 600nF (15V)

I'd be very grateful if anyone has some advice about ratings for any of these components. I know how to wire this up but I don't know what currents and voltages each of the parts needs to withstand.

PS: I've already experimented with removing the 22k NFB resistor and - wow! When cranked, it really makes the champ more dynamic and touch sensitive and an absolute joy to play. Long-term I'll put it on a switch though. It's also nice to have the option of more clean headroom.

[stokes]

Are you talking about modding a vintage 5F1 or a clone?The ratings on the switches are unimportant,any good quality toggle switch will be okay.The ratings in the tone circuit are also not an issue,any orange drop or siver mica will be fine.As for the pot,a standard 1m 1/2 watter there.Why would you want a "cathode resistor bypass".If you bypass the resistor the tube will effectively shut off.

[mcgruff]

Thanks for the reply. Yes it's a 5F1 clone. Funnily enough I installed all the mods just yesterday and it worked out really well.

The Princeton tone knob is nice. Sometimes get a little bit of hiss when it's turned up full but I used a ceramic for the 470pF cap rather than silver mica: do you think that could be problem? It's not really bad but I'd want to tune it out if I could.

The idea of the cathode resistor bypass is to add extra gain by connecting a capacitor in parallel with the resistor. I've installed switchable options for 22uF/1uF/none on V1a and 1uF/680nF/none on V1b. 22uF gives a full-bandwidth boost, 1uF boosts low mids and up, 680nF mids and highs. It's a really worthwhile mod, IMO. The high-pass options in particular are nice to create a different flavour of overdrive.

With NFB off, the amp has a completely different character. The tone doesn't sound a lot different but the guitar suddenly feels much more dynamic and responsive. I think it's a really important option to have but I'd also want to have it on a switch so I can go back to normal NFB-on mode from time to time. When you don't need it, too much sensitivity just makes it harder to play.

I guess exactly what you get out of these mods depends on your own guitar (ie pickups) and cab. The ones which add more high-end maybe won't do much through a dark speaker or, if you have a bright guitar, that's probably not the direction you want to go in anyway. For me, and a dual-humbucker 335, they worked really well.

[Bruce / Mission Amps]

Are you talking about modding a vintage 5F1 or a clone?The ratings on the switches are unimportant,any good quality toggle switch will be okay.The ratings in the tone circuit are also not an issue,any orange drop or siver mica will be fine.As for the pot,a standard 1m 1/2 watter there.Why would you want a "cathode resistor bypass".If you bypass the resistor the tube will effectively shut off.

I think he should be doing is
holding the two different bypass caps from ground with two "switched", by-passable resistors.

[mcgruff]

This should explain it:

[Enzo]

Those are clear, but they will pop when switched, or at least probably will.

Good practice would be to put a high value resistor like a 1meg in parallel with each switch. That will keep the caps charged, but the resistance will prevent them from affecting the circuit, so they remain out of circuit. When the switch is turned on, the resistor is shorted and the circuit works as you expect.

[mcgruff]

Great tip - thanks.

[stokes]

Sorry,I misinterpreted what you meant by by "cathode resistor bypass".You mean a "cathode resistor bypass cap".