Quote:
Originally Posted by Leon Crampin
Zapping an otherwise good valve is too risky.
|
I presume the zapping comment is related to connecting a current supply from cathode to heater with the aim of passing sufficient current through an offending metal whisker that may have slowly developed through the heater oxide coating, and hence melting the whisker until a high resistance path occurs?
Given that the valve has had a long service life, the fault scenario of a metal whisker developing would appear a high likelihood, as it is a known long-term failure mechanism, especially for a cathode that has elevated DCV from the heater.