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

Subject: Re: [Amps] 8877 - HV with heater, or later?
From: Fern Rivard via Amps <>
Reply-to: Fern Rivard <>
Date: Mon, 23 Jan 2023 20:30:34 +0000 (UTC)
List-post: <>
*The alpha 9500 amp with single 8877 has warm up time of 180 seconds. 90 seconds is definitely too short a delay.*

*Fern  VE7GZ*

On 23/01/2023 12:35 p.m., Victor Rosenthal wrote:
Interesting that the 8877 datasheet gives a warmup time of 90 seconds, but doesn't say whether you can apply plate voltage.

On the other hand, the 4CX1000A datasheet explicitly says that no other voltages should be applied during the warmup period.

Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5

On 23/01/2023 19:26, Jim Barber 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.

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