>In <200207060110.g661Amx23986@nimbus.heaven.net>, on 07/05/2002
> at 06:13 PM, Richard <2@mail.vcnet.com> said:
>
>>>>>Some time ago a guy told me he was substituting the
>>>>>4-400A tube in his Swan Mark 1 amplifier instead of
>>>>>using the 3-400Z tube. He had a large supply of the
>>>>>4-400A tubes on hand and said they were working very
>>>>>well in the Swan Mark 1 even though it was designed
>>>>>around the 3-400Z tube. Is this an ok thing to do in
>>>>>the long term?
>>>>>73,
>>>>In g-g, at 0v bias, the 4-400A needs c. 3400V to idle at the requisite
>>>>75mA.
>>>
>>>So add some bias already. <g>
>
>>Adding bias to raise the ZSAC to 75mA/tube with 3000VDC would require
>>connecting a 1A, 1 - 3 volt neg. polarity PS to the CT/cathode return.
>
>[grumble-grouse] . . . Oh, I see, a trivial task.
If I were going to the trouble, I would add c. a potted 200V/1A
transformer in series with the extant secondary. This would add enough
DCV to make it fly with zero V bias.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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