With NOS valves, both 3CX and 4CX, I have found it helpful to run with heaters only for 24hours before applying high voltage; I understand that the getter on these is at the top of the cathode column and is activated by the heater- it cannot be activated by RF induction, as in glass envelope valves, of course.
I neglected this precaution, once- with one of a batch of NOS Eimac 3CX800A7s. Result, instant vaporisation of high voltage current limit resistor and destruction of valve. Following the procedure described above for the others in the batch, I had no failures.
I’m no valve expert, so experts please correct me, if I’m wrong.
Alwyn Seeds, Director
114 Beaufort Street,
SynOptika Ltd., Registered in England and Wales: No. 04606737
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