[AMPS] Alpha H.V. Rectifier Source

[Paul Christensen]

In my continued pursuit of finalizing my Alpha PA-70V rebuild, I discovered
that a nylon H.V. feedthrough jack between the power supply and R.F. cabinet
is causing my H.V. flashover, not the 3CV1500A7 as I originally suspected.
In place of the nylon feedthrough, is now a glazed-porcelain James Millen
"beehive" type, which I filled with 100% silicone clear RTV.  If this
doesn't take care of 4KV leaking to ground, I give up.

I also noted that upon my last flashover, my glitch protection circuitry did
its job: I replaced a string of three 1N5408 diodes, not the plate ammeter.
Unfortunately, a 50-ohm @ 50-watt H.V. lead resistor I recently installed is
AFTER the feedthrough.  However, another failure occurred.  One of the four
H.V. diode "blocks" is shorted.   It is marked...

SEMTECH  "SLIMPAC"
SCH 5000

Does anyone know if Alpha/Power is still carrying these?  I believe my 77Dx
used the same type.  If I cannot obtain an exact replacement through a web
search, would it be prudent to simply replace all four with a newer type?
Does the "infamous" K2AW Silicon Alley have these?  I measured the forward
and reverse resistance of the remaining three H.V. "blocks" and they all
measure identical.  Is it safe to assume that they are not on the ragged
edge of failure?

In my search for a spare vapor-cooled 3CV1500A7, I not only found one
new-in-the-box, but I also "coerced" the seller into letting me purchase his
new Alpha PA-70V which is in its original box with only a few hours on it.
This is one of the few times when I really got lucky!

To be safe, I'll probably change out the H.V. feedthrough, H.V. wiring and
perhaps upgrade the plumbing as I had recently done using all Teflon
components.  Does anyone know the life expectancy of 20KV silicon rubber
high voltage wire?

-Paul, W9AC



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