> Subject: 2 pcs returned 8875 S/N G8AD-241 and F8VD-428J, for evaluation.
> Reference: Your letter dated 21 January 1986; EIMAC RPA #SC-2303.
>
> Dear Richard:
>
> Your letter about parasitics is quite interesting, and it appears your
> two tubes have had the same trouble. The emission was poor on test, and
> consequently other test results looked bad. The tube engineer then cut
> them both open for an internal examination.
> Both have been badly overheated internally, the apparent result of an
> oscillation condition. The grid in these tubes is gold plated and if
> overheated the gold vaporizes off, of course, and some of it inevitably
> lands on the oxide cathode, and that poisons emission.
What you always conveniently leave out is that in YOUR initial report to
Eimac you said you "thought the tubes oscillated, and that overheated the
grids".
The response to YOUR claim you suspected there was an oscillation, from a
guy whose job it was to handle customer letters, included the sentence:
> Both have been badly overheated internally, the apparent result of an
> oscillation condition.
If I take my truck into Ford with melted main bearings, and say to the
service writer "I think I ran it out of oil"...and if that truck has a
busted oil pump....Ford's response would almost certainly be "apparently you
ran it out of oil".
It very interesting how you manipulate answers to fit your fascination with
oscillations. But the fact is it is impossible to tell WHY the grid was
overheated, but the particular amplifier you selected has NO grid current
protection and some models did not even include a grid current meter!!!
73 Tom
|