[Amps] 8877 - HV with heater, or later?

[w2cqm at juno.com]

8877  HV can be safely applied during any period of the start up  (initiation) cycle without consequences.  However,  it's positively essential  to series install a 180 second (NO) delay  relay in the antenna changeover circuit to inadvertently prevent the premature application  of audio excitation prior to meeting minimum factory heater warmup  parameters.. If available, additional (unused) delay relay contacts can be utilized for warmup,standby, and delay satisfaction neons. Ron W2CQM/3  

---------- Original Message ----------
amps at contesting.com>
To: Jim Barber <barberaudio at gmail.com>, Amps group <amps at contesting.com>
Subject: Re: [Amps] 8877 - HV with heater, or later?
Date: Mon, 23 Jan 2023 17:56:49 +0000 (UTC)

The 3cx800 tubes are in the same class of tube as the 8877 and no ham amplifier using it holds of the plate voltage.  Same goes for 8877 except for the the Ameritron AL1500.  s long as the cathode does not see drive until warmed up that’s the only requirement.  K don’t think Eimac even suggests holding g of plate voltage but of course that are definite about no drive power being applied.  I suppose if you hold off the HV it could be considered an extra precaution measure.  


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On Monday, January 23, 2023, 12:26 PM, Jim Barber <barberaudio at gmail.com> wrote:

I'm overhauling a vintage 8877 amp, and it occurs to me that I've never
seen a definitive answer to this question:

Should HV be held off on a 8877 until the heater warm-up timer expires?

Not that I claim any particularly deep or insightful knowledge of such
things, but it seems to me that if the cathode has cutoff bias that it
wouldn't make any difference when B+ is applied.

I did find a reference to this question in the amps archives, but every
design I've looked at recently holds the HV off until the cathode is ready
to go.

Maybe there's more to it than I'm seeing? I may use a separate HV switch on
the front panel anyway just to allow for gettering, but I'd still like a
consensus on the question.

Thanks!
Jim N7CXI
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