[Amps] 3-400Z Tube problem

[Richard]

>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.  
end