>I have a 3-400Z tube that has 100ma of plate current
>when it is supposed to be cut off. I verified this by
>installing a spare tube. There is a 47K ohm resistor
>in this Swan Mark 1 that cuts off the tubes in
>stand-by.
>
>Is this tube trash now or is there something I can do?
Measure the grid-fil V when the amp is in standby and the fil is lit. If
the result is 0v, you probably have a tube that shorts when the fil is
hot/expanded. [See *QST*, September, 1990] I have been able to unshort
c. 30% of such tubes with a 11G centrifuge.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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