75 volts AC on chassis

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Hey DJK,

I checked the resistance: RCA outer to speaker negative and it is high and variable. It starts about 3k and floats as I measure it, perhaps a capacitor charging?

I turned it on and it hummed so I grounded the RCA outer to the secondary ground at the capacitor bank. That removed the hum.

I touched it and measured voltages on the case last night and everything was fine.

This morning it shocked me again but I only meaaure the one potential between the case and wall ground that is supposed to be there when its plugged in out of phase?

Puzzled?
 
The channel that does not have the DC trim pot has a 0R5 resistor beteen the input ground and the speaker ground.

Sounds like yours has burned open from a ground loop.

I would replace the 0R5 resistor with the following composite part:

A 10 ohm 1/2W resistor with a pair of reverse paralleled 1N400X diodes a 0.047µF ceramic disc all soldered in parallel.

To set the bias, lift one fuse per channel, insert ammeter, adjust bias to 350mA, then do the other channel.

Sound Values in Ohio has new PC19 cards with the DC trim pot and they have been going for ~$50 on eBay.
 
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