[R-390] Tube Failures

[Gord Hayward]

The heater to cathode short is a good one to know about.  I had a 
humongous amount of hum when I
turned the limiter on, but not when it was off.  I eventually found the 
problem to be the tube.  It tested
OK (previous posting about testers with forked toungues is true!) but 
when I replaced it the problem
vanished.  With the high impedance circuit, even miniscule AC leakage 
into the cathodes was enough.

73 de Gord, VE3EOS.

-- 

Gordon L. Hayward, Ph.D., P.Eng.,
Associate Professor, Biological Engineering,
School of Engineering, University of Guelph,
Guelph, Ontaro, N1G 2W1.