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[Amps] 3xc800a7, 3xpx800a7 plate voltage?

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Subject: [Amps] 3xc800a7, 3xpx800a7 plate voltage?
From: "Jim Garland" <>
Date: Tue, 13 Sep 2011 08:09:28 -0600
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I'm designing a dual voltage HV power supply and am ready to order the plate
transformer. I'm a bit unsure about the best choice of voltage ratings,
however. One primary tap of the transformer would be suitable for three
3CPx800a7 tubes. For that tap, I'm thinking I'd like a no-load (except for a
100K bleeder) DC voltage of 3650V, which would drop down to about 3300V at
1.8A. (That would correspond to a transformer secondary of 2600Vrms.) Does
that seem like a reasonable choice for the 3CPX800a7? Obviously I can go up
or down, if necessary.


The other winding would be for three 3CX800a7s or GU74Bs, and here I'm
thinking a no-load voltage of about 2800V, dropping to about 2500V at 1.8A.
I know the original specs for the 3cx800 specified a maximum plate voltage
of 2250V, but that was subsequently increased to 2500V. I hear conflicting
stories about the maximum voltage for the GU74B, but most folks put it at
about 2500V. I'm not sure how much I can push the voltage rating on the
GU74B. In any case, I'd appreciate opinions on the subject.



Jim W8ZR

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