Peavey VK112 how critical is capacitor

[Tech. Tom]

Hello. I am working on a Peavey VK112. C201 which is across
the AC input to the bridge is shorted. It is a .01/1KV

I don't have that value, but I do have a .001/1KV
How critical is that value and is the purpose to filter out noise
or what is the purpose?
Thank you.

Tom

[tedmich]

That cap is typically referred to as a line safety cap (X cap) and is usually a special design which is designed to fail open. The spec for this cap (seen if you left click on it in schematic) is -20% to +80% so it probably measured higher than 0.01uF when new. It helps to filter out line noise/RF and should probably be replaced with a similar value, like this one:
CK45-E3AD103ZYGNA TDK | Mouser
Your 0.001uF cap will filter some, some amps don't even have these, but if you hear RF you should probably up the value.

This type would also be suitable:
http://www.mouser.com/ProductDetail/...fUOwbK3NPbs%3d
http://www.mouser.com/ds/2/427/vy2series-349088.pdf

[Jazz P Bass]

Being an 'X' type capacitor, I was real surprised that the OP stated that it failed short.

[g1]

It's the class Y type that are designed to fail open (never short).
Class X is line to line, where there is no chance of electric shock if it fails. And if it shorts, the fuse/breaker blows.

Class Y is line to ground, where there is danger of electric shock if it fails. These are designed not to short.

About halfway down this article, there is a section called "types of safety capacitors" : ABC's of Safety (Interference Suppression) Capacitors for Tube Radios

[J M Fahey]

Anyway it's neither ClassX nor ClassY , but a regular .01uFx1000V
When written this way, 1000V means 1000VDC

Like any coupling or decoupling cap insed inside an amplifier, which runs on DC .

Line rated caps, even the old UL rated deathcaps wre typically rated 250VAC , have that printed on the case, and are accompanied by a (!) symbol inside a black triangle, meaning: "Safety critical component, replace only with same type and rating" or something very close.
And 250VAC in that case means: "officially rated to work with AC lines up to 250VAC" so they don't have to separately test caps rated for 220/230/240V lines, nothing beyond that.

Being on the secondary, that .01x1000V cap needs not be X or Y rated.

Doesn't hurt, of course, and I have seen such caps (casually in Marshall amps) used in Zobel networks in SSamps, where they will hardly see 40VAC (audio) , if that much.

I guess Marshall buys them by the containerload (not kidding), for peanuts.

[Jazz P Bass]

Hartke utilizes a plain jane cap after the transformer on the high voltage side.

I have seen them go short.

Aside: Yeah, keep on putting fuses in it, maybe it will fix itself.