> From: Rich Measures <measures@vc.net>
> In commercial FM broadcast service, 8877s typically last 20,000 hours.
> 33 months in amateur radio service probably amounts to under 500 hours of
> use. During the last ten years, I've tested a number of kaput 8877s
> that were removed from Alpha 77s. Most of the failures were caused by
> gold sputtering from the 8877's grid.
More nonsense designed to sell magical "kits" .
8877's, both in commercial and amateur service, had a very high
failure rate through the 80's and early 90's. Over 90% of some
batches of tubes would fail with only a heater off-on cycle test
within the first week of cycling.
GE Medical, Picker, Harris, ETO, Ameritron, and other ALL shared the
same problems...and they occurred in amps that lived happily for years
before Salt Lake made the tubes, and for years again after the
problems were cured.
The failures were related to heat dam and material contamination.
> - Around June,1990, the Alpha 77 at W1AW was reportedly sold at an
> in-house QST auction because of its high tube failure rate. Mark J.
> Wilson, AA2Z, bought this amplifier. According to our records, during
> the last week in June, 1990, he telephoned me with the news of said
> purchase, and ordered low VHF-Q/low VHF-Rp suppressor retrofit kit s/n
> 1252. I asked Mark why he felt the 8877 failures were related to
> parasitic oscillations. He said because he read the article in the
> October, 1988 issue of *QST*.
Rich,
If Mark was such a "believer" in the occult science of
nichrome parasitic suppression ...why did he apologize in QST for
not "checking out the technical accuracy of Measures' articles BEFORE
publishing them" ?
73, Tom W8JI
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|