[R-390] GFI and the 390's

[wli]

Steve:

The GFI trips because the original AC input module had large .05µF caps from hot and neutal to ground. This was done to prevent any RF from getting out; a security issue during the Cold War. Such a large cap will pass enough 60cps current to trip any GFI.

The reason I gave you a modern EIC type AC input module, is that the modern ones have a much smaller line bypass caps (2200pF) so that AC current passed is much lower, not enough to trip a GFI. In my Capehart, I removed the original AC input module, filed the back panel just enough to clear a brand new EIC module, and rewired the AC circuit.

Of course, the unit's chassis should be securely grounded separately.

There is a lively extensive dicussion re GFI's and grounding in *Pearls* in the pwr supply chapter (shameless plug).

Thanks

W. Li