Rejuvenating tubes with thoriated-tungsten filaments.

[Kenneth G. Gordon]

The method I am about to describe was commonly used 
back in "the day". I first read of it in an old handbook for 
Marine Radio Operators, and have used it successfully on 
power transmitting tubes. I once did this to a dozen 304TLs 
which had come out of a chemistry department NMR 
machine in which they were used as shunt-regulators. 
These were so flat they wouldn't draw any plate current 
with 3KV on the plate and NO bias. After the procedure, 
they were used successfully for many years afterwards in 
amateur KW linear amps.

The procedure is as follows:

1) Apply 2.5 times the normal filament voltage to the tube 
with all other electrode voltages removed for 1 minute.

2) Reduce the voltage to 1.5 times the normal filament 
voltage, and let "cook" for 1 hour.

3) Test the tube.

4) If the tube is not up to specifications for emission, re-do 
the procedure.

5) If the tube still does not exhibit specified emission, 
discard the tube.

Lessee...for a 572B (which DOES have a thoriated-
tungsten filament, BTW), that means 15.75 volts at around 
12 amps.

Hmmm....well, it can't hurt the shot ones...

I'll report back when I try it.

Ken Gordon W7EKB

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