While that voltage is permissable for the 3CPX it will certainly run down
the emission faster if run at the 800ma or so that they will easily load to.
Load too lightly and you are asking for bandswitch or Tune cap arcing.
For my LK-800 upgrades Ive settled on around 3000V and have used as much as
3500V on request. An extra 400W per tube might be needed on 6M EME or 160
The Original 3CX spec sheet was 2500 and quickly pulled and reduced to 2250
per FCC "request"
----- Original Message -----
From: "Jim Garland" <email@example.com>
Sent: Tuesday, September 13, 2011 10:09 AM
Subject: [Amps] 3xc800a7, 3xpx800a7 plate voltage?
> I'm designing a dual voltage HV power supply and am ready to order the
> 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
> 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
> 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
> 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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