The Fender KILL SWITCH (.047 cap to ground)

[timrichter9]

Ok.

So before I knew about amps (1993), I inherited a 1964 Twin Reverb that a buddy found at an auction in Massachusetts for $80...(Yes, $80).
Complete except grillcloth and logo, he gave it to me (he was my keyboard player and didn't want it).

I had a guy rework it in 1994 or so, and he put all new 100k plate resistors, filter caps, etc.

HOWEVER, I noticed he put a three prong grounded cord in it BUT left in the 0.047 cap that was the old GROUND switch cap!!!!

Unless I am missing something, isn't this dangerous??
I was always told to immediately get those out of BF amps.

What is the purpose of this cap?

To be safe, I cut it out and ran the wiring so that the fuse and mains switch are on the same leg of the tranny tap.

Thanks
Tim

[Jazz P Bass]

The 'Death Cap' was installed to help filter out any line induced hum.
(The 'Death' part is "IF" the cap fails shorted & the amp is a two wire setup, the chassis can become 'hot')
In the either or switch configuration, with a two wire cord, it should be removed.
In a three wire setup, I do not see an issue.
Now in the mid 70's Silverface amps they went to an on-off-on type switch.
In the middle position the cap is out of circuit.
Those I leave alone.

[timrichter9]

Can someone tell me the theory about how this works and why it doesn't kill you (or blow your home circuit breaker) when you install a 3 prong AND leave it connected?
My understanding is that when there was 2 prong power, there was no earth ground back then. Doesn't a cap PASS ac voltage?
If that is the case why isn't the cap acting as a ground when engaged? If you now have three prong wiring and the cap is left in the circuit.
If you connect it to the HOT lead from the wall, are you not presenting a short circuit to the wall outlet??
Tim

[Jazz P Bass]

The reactance of a .047 ufd capacitor at 60 Hz is 56.4 Kohm.
If shunted across 117 vac the resulting "leakage current" is 2.074 ma, definitely enough to feel as a shock but probably not enough to kill you, unless you had other medical issues.
Y rated caps are the only ones currently used for this purpose.
They are designed to fail open circuit.

[Enzo]

It was a death cap if it was SHORTED and the side of the mains it was switched to was hot. THEN it could make the chassis hot. And that was potentially deadly.

When your chassis is grounded with a three-wire cord, the chassis is grounded. Hard for it to get hot that way. If the cap shorts, if you have it switched to the neutral side, nothing happends, the cap is wired between ground and neutral. If you have a shorted cap and it is switched to the hot side, then it shorts the hot to ground, which will blow the breaker.

If the cap is not shorted, then the grounded chassis doesn't care what it does. So it is a hell of a lot less dangerous than a two wire amp.
I snip them out, myself.

[R.G.]

If the cap is not shorted, and switched to the line/hot side, it leaks current into the chassis, and can cause hum issues within one amp and BAD hum issues if you're trying to ride two amps at the same time.

If an amp has a three-wire cord (and all amps should, whether it's original or not), then there is no upside to the cap being there, only less-bad and more-bad situations.

Enzo's right - clip it out of a three-wire amp. If the amp doesn't have a three-wire power cord, put one in. Then clip the cap out.

[g1]

If an amp has a three-wire cord (and all amps should, whether it's original or not), then there is no upside to the cap being there, only less-bad and more-bad situations.

What are mfgrs. of new amps using them for? RF prevention? I have noticed them (class X of course) in some newer amps.