What does Eimac say about parasitic oscillations?
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VARIAN ElMAC, 301 Industrial Way
San Carlos California 94070 1 U.S.A. / Tel. (415) 592-1221 TWX 910
376-4893
February 18, 1986
Mr. Richard L. Measures
6455 La Cumbre Road
Somis, CA 93066
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.
Though your tubes are quite old (mid-1978 vintage) we will replace
them in the interest of good user relations. We will scrap the two
you sent in here, as we have to be sure they are out of circulation
when we replace. Good luck in your continued operation.
Sincerely, WILLIS B. FOOTE, Chief Specifications Engineer, Power Grid
Division.