I have a pair showing odd behaviour. I'm interested in your comments. These
were bought at very modest price, reflecting their 87/8 date codes and
untested state (all I could do was check heater continuity and electrode
shorts - both were ok). I trust the source, who said they were pulled from
working equipment. They sat for a long time while their project didn't
happen, then I got a chance to test them in a friend's 6m PA. One was just
fine, the other did nothing at all and showed an o/c heater when checked.
They went back on the shelf for a year.
Recently I wanted to find the good one, but hadn't marked which it was. The
DVM said BOTH had good heaters! After much fiddling, I found that they were
both intermittant - the 'right' way up, and a tap with a finger made both
ok. Other positions and harder tapping would make them go open, one more
readily than the other. Having got connection, I ran the heaters up very
slowly, then at full voltage for 24 hours. Both had stabilised as good with
normal handling. A few weeks on, and the worse one has gone open again.
Some aspects of this are blindingly obvious, but I can't find a picture of a
heater/cathode assembly anywhere to satisfy my curiosity and let me puzzle
whether they might prove useable if they were settled in a stable
environment. Maybe I'd need to build in a solenoid tapper as part of the
turn-on sequence :-)
Steve
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