Gary Schafer wrote:
>
>
>>
>
>I should have posed the question differently. What I was really asking
>was: What about applying high voltage to a tube when the filament is
>not powered up? Isn't that harmful to the tube?
>
As far as I know, high voltage itself is not harmful to the tube in any
way. What is actually harmful is a demand for more electron current than
the filament or cathode is capable of emitting, because it is not fully
up to temperature. So the tube remains safe with HV applied if:
* the filament/heater is switched off and cannot emit any electrons at
all; or if
* the amplifier is not allowed to transmit while the filament/heater is
heating up or cooling down - in other words, the normal RX-state cutoff
bias is applied (resistor-type cutoff bias will meet this need).
--
73 from Ian G/GM3SEK
http://www.ifwtech.co.uk/g3sek
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