Since the 8877 is rated to 3000V in Class C AM service I wouldnt worry about
4200V or so in standby as long as its a known good tube that has been tested
at over 3KV.
The problem at over 3500V in operation is that it can get a bit unstable
unless good layout and construction are followed.
Use the Eimac GG socket assembly or make one similar using the Johnson
socket and a finger stock grid ring. You should also load it heavily and
just accept what comes out at whatever drive level is used. Light loading is
asking for trouble. Also use a parasitic suppressor....even if not
needed....no sense asking for trouble over a $2 part.
Ive built a few 6M amps running at around 4200V key down and all the smoke
stays in the output coax (-;
Carl
KM1H
----- Original Message -----
From: "Charles Bibb" <zedkay@telepak.net>
To: <amps@contesting.com>
Sent: Saturday, June 30, 2012 5:33 PM
Subject: [Amps] 8877 Plate Voltage
>
> Starting a new project.
>
> I'm collecting parts for a new HB 8877 amp. One really nice part
> that I've recently acquired is a massive transformer for the HV
> supply. This transformer came out of a commercial FM transmitter
> that ran an 8877 at 1 kw continuous duty.
>
> While that power supply used a choke-input filter in the HV supply, I
> want to run the higher voltage obtained by a cap.-input filter. With
> a cap.-input filter, however, the HV supply will be a tad over
> 4150VDC, using the "best" primary taps available. Can wire for
> higher, but not any lower.
>
> My question(s) is/are: How critical is Eimac's "absolute maximum
> ratings" as far as plate voltage is concerned. I know that under
> load, with acceptably regulation, the plate voltage will be about
> where I want it at 3800V. Is the slightly-too-high potential on the
> anode under no-load a problem? Or, should I just not worry about it
> and "let 'er rip, tator chip".
>
> Anyone have experience here?
>
> 73,
> Charles - K5ZK
>
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