Tom said:
>It is almost like a black art, as anyone who has been around tube
manufacturing would know. Even small >receiving tubes operating in
low-voltage systems were the most likely components to fail in old tube
>equipment.
I suspect one problem is that a lot of manufacturing 'know how' has been
lost with the general reduction in tube manufacture. Interestingly, though,
I have had more semiconductor failures in the last 20 years than tube
failures. My amp has a screen supply with a 5R4 HV and 6X5 bias rectifiers,
a 6L6, 6SJ7 and VR150 regulator, and a pair of 4-250A in the amp itself.
The transceiver has a 3 6146Bs and a 12BY7. My various bits of test gear
use 18 or 20 tubes. No failures in 20 years, while only last week, I had to
replace failed op amps in two bits of gear - the HP spectrum analyser and a
Marconi instruments RF generator. The transceiver has had 3 FET's fail,
too.
Although I did fix a transceiver for a guy last week which had a dying
12BY7 - funny thing was that it resulted in low drive on the LF bands but
OK on 15 and 10....
73
Peter G3RZP
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