Voltage rating on TONE capacitors for 5E3 build

[chuckulaa]

Hello,

I just had a quick question, which I believe I know the answer to, but I was hoping someone would check my thought process.

I would like to use PIO caps for the two tone caps in the 5E3. These are the 500 and 5000pf capacitors off the tone potentiometer. These can be had for cheep on Ebay (K-40Y-9 type), but they are only rated to 200V.

These capacitors are protected by the DC blocking coupling capacitors from the plates of the 12AY7. The plates on the 12AY7 are at ~350V. The tone caps are protected by the 0.1uf DC blocking caps, therefore I would expect the DC voltage on the tone capacitors (the screen of the 12AX7 first gain triode) are much less than 200V.

Could I use caps rated at 200V for the tone capacitors for the 5E3 without any problem?

[Firestorm]

Sounds good on paper. But capacitors are funny things; they don't pass current (not even AC) they sort of shunt it around themselves as one plate charges relative to the other. You're not going to have a big enough signal swing in the preamp, tho, to do any damage, so go for it. Caps do wear out. Especially PIO.

[katopan]

Yeah, they'll be fine. Those caps are sitting with zero volts across them. You've also got to consider what happens on power up, but that's OK in this case too.

[chuckulaa]

Thanks for the replies.

I have been flooding this forum with questions lately. I appreciate everyone's input.

[rp]

As you have a simple amp there with just 5 caps you might want to a/b it with a set of cheap film caps like 150s, 6PSs, 225s after you try the PIOs. Live with the PIOs for a few weeks first then do the switch and give it a few weeks of playing. I've never liked PIO in guitar amps but all I ever tried were old Sprague Vitamin Qs. Seemed a little too polite and blah to me. I didn't do extensive testing with oils either. I've looked in a zillion vintage guitar amps and never seen oil caps, and rarely even in vintage hifi of any caliber, they seem to show up in old, expensive test equipment like scopes. I'd also guess that from the '50s onward oils are not paper but film/foil in oil.

Don't know what the appeal is to guitar builders. Feel free anyone to point me towards the light.

[rock_mumbles]

Hifi amp guys are all over K40Y-9 and hate K42Y-2 caps ... in a guitar tone circuit it's the opposite, the K42Y-2 are considered better.

The K40Y-9 caps are supposed to work and sound better with high voltages on them ... the K42Y-2 sound better in a guitar tone circuit ... I'd guess the same would hold true for a tweed tone control

I've used some K40Y-9 as coupling caps, but I only use one maybe two in an amp ... I mix them with poly caps.

[chuckulaa]

I have really liked PIO for tone caps in my guitar. It gives my guitar a nice woody organic feel. I assumed I would like them in the tone circuit of my amp. I wouldn't use them as direct coupling caps in my amp. I would save these positions for polyester and polypropylene type caps.

Do they make poly film less than 1000pf? For these values I thought they only made PIO, silver mica, and ceramic type caps.

I wAs specifically thinking that a PIO would be good for the 500pf cap in the bright circuit.

[boots]

I also haven't liked PIO caps in my amps either. I think they sound OK, but not Great. Rather sterile. Give me a Sozo or Astron any day.