[ARC5] Quick sensistivity comparison

[J. Forster]

It depends on the source impedance of the grid bias supply.

On my Triplett, it is pretty stiff. The GAS test is done by inserting a
series 1 MOhm in the grid circuit and monitoring the plate current change.

During degassing, the grid bias is left in the low impedance mode.

-John

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>> On 13 Jun 2013 at 4:45, J. Forster wrote:
>>
>>> Ken,
>>>
>>> It might be worth checking for gas in the tubes.
>>
>> In which? Do you mean the 12SK7s? Or in all?
>>
>>> I'd suggest running them for several days at nominal filament, nominal
>>> plate, and biased to conduct about 10-20% of rated plate current to
>>> allow the getter to clean up anything that has diffused into the tubes
>>> in the last 70-odd years.
>>
>> OK. I can do that easily enough.
>>
>>> After that, try the NF test again.
>>
>> OK. Will do, John. Thanks very much for the suggestions.
>>
>>> YMMV,
>>
>> Yes! Won't it just! :-)
>>
>> Ken W7EKB
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> A gassy tube will drive the grid more positive and increasing its gain and
> at some point exceed dissipation ratings.
>
> Carl
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>