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[Amps] Alpha PA-76A bleeder/equalizer resistors

To: "Amps@contesting.com" <Amps@contesting.com>
Subject: [Amps] Alpha PA-76A bleeder/equalizer resistors
From: Jim Barber <audioguy@q.com>
Reply-to: audioguy@q.com
Date: Wed, 09 Oct 2013 17:57:23 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I'm working on a PA-76A, doing the obvious stuff - replacing the filter caps, the tantulum timing cap, the low-voltage filter etc. All well and good.

What raised my question is the bleeder/equalizer resistors across the HV filter caps. Apparently stock, each cap has two 120K 2-watt carbon comp resistors across it in parallel. With 2400V B+, that looks like 60K ohms across 400V, or ~ 2.7 watts per 4-watt pair. All the resistors are either open or close to it, interestingly enough.

First, I looked at a few posted images on the internet. Yep, it looks like that's what Alpha used, although the schematic I have says each "unit" should have 220K @ 2 watts across it...

So: Inquiring minds would like to know what to use to replace them?
I'm thinking maybe 2 220K Ohmite OY (in parallel of course) across
each? That would lower the bleeder current, but I'm not seeing a huge problem with that at first glance. ?

For whatever its worth, the original problem with the amp was that there was substantial 120hz hum modulation on the output signal. Since this is an original two-holer, I'm hoping the problem is strictly in the B+ supply since a cathode-filament short in one of the 3CX400's would mean either a retrofit or something equally undesirable...

Tnx es 73,
Jim N7CXI
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