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

[Fern Rivard]

*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.
>
> https://frank.pocnet.net/sheets/140/8/8877.pdf
>
> On the other hand, the 4CX1000A datasheet explicitly says that no 
> other voltages should be applied during the warmup period.
>
> https://frank.pocnet.net/sheets/140/8/8168.pdf
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco/
>
> 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.
>>
>> Thanks!
>> Jim N7CXI
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