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

To: "'Jim Barber'" <>, "'Amps group'" <>
Subject: Re: [Amps] 8877 - HV with heater, or later?
From: <>
Date: Mon, 23 Jan 2023 18:59:27 -0000
List-post: <>
The GM3SEK Triode controller does delay the HT switch on.

"When the warm-up period is complete, the ANODE LED will go out, the HV CTRL
line will
come up and the HV mains relay will close. (At this moment, the GRID/HV LED
will still be lit
because there is no HV yet.)

A few moments later, when the step-start has operated and the HV comes up,
LED will go out and the green READY LED will come on."

Iv'e built several 8877 amps ( one using two paralleled) using this board
(now discontinued) and all are still working well. I have to say I still get
the collywobbles when the 3-minute timer runs out, the relays click in and
the HT comes up. I'm always expecting a bang! 


-----Original Message-----
From: Amps <> On Behalf Of Jim Barber
Sent: 23 January 2023 17:26
To: Amps group <>
Subject: [Amps] 8877 - HV with heater, or later?

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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