Pioneer SM-83 stereo amp

[gui_tarzan]

It's not a guitar amp but it's a tube amp so here's my question:

I re-capped the power and bias sections and it sounds good, but after using it for about ten minutes and shut off for five, this cap exploded. It's across the power switch and not connected to anything else so I'm wondering if it just expired due to age?

You can't see it but I brought it back up initially on a light-bulb current limiter and didn't have any issues with anything else.

[cbass]

Death cap ?possibly needs a three prong cord?

[gui_tarzan]

I thought about that but the owner wants to keep it as close to stock as possible since he's going to re-sell it when it's ready.

[Leo_Gnardo]

A cap in that position is intended to try and minimize arcing damage to the power switch. (HOW that's supposed to work ? ? ? I'm sure one of our experts will fill us in.) In any case it's not an absolute necessity, and if you must have something there a competent film cap should do just fine, say orange drop rated 600V minimum. Manufacturers in an effort to cut costs usually used cheap ceramics. FWIW on those rare occasions I have to see gear that's been in a lightning strike, it's these across-the-switch and "channel-grounding" AKA "death" caps that seem to wind up shorted.

[martin manning]

With a cap across the power switch the electrons coming down the wire are duped into thinking that there is still a way across as the contacts are opened up. By the time they figure it out (i.e., the cap charges up), the contacts are separated by a distance that's too large to jump.

[Phil_S]

If it is so old that it doesn't have a polarized plug, tell him the cord needs to be replaced because it's unsafe. Put in a 2-prong polarized and make sure the fuse is wired to the hot leg, and put the fuse before the switch. Then you can lose the cap. Anyone who thinks this shouldn't be done? This shouldn't affect the vintage vibe.

[cbass]

Is the control panel isolated from the chassis?
The thing about the polarized plug is there is no garuntee that the wall receptacle is wired correct

[vibratoking]

I thought about that but the owner wants to keep it as close to stock as possible since he's going to re-sell it when it's ready.

Yup, cbass is right, 3 prong plug. Anything else is irresponsible IMO.

[Phil_S]

I should know better. Sorry about that.

[gui_tarzan]

Yeah, I know that so I asked the owner if I could swap it for safety reasons.

[RWood]

An old electric plug will not keep amp value higher as it is common knowledge that they contain no MOJO!
Everyone I know who buys vintage amps have cords, caps, and drifted resistors changed as soon as they buy them.
Old tweed and hardware is a different story.

The phrase "All original" means different things in guitar and amp contexts. I.E. All original 1957 Les Paul = Great.....All original 1957 Deluxe = likely needs a little work!

My two cents...Randy

[cbass]

[quote="vibratoking"]

Yup, cbass is right [quote]

There's a first time for everything

[gui_tarzan]

I got a response from him last night saying he appreciates my recommendation due to the safety factor and to go ahead with the replacement.