>Herb,
>
>I saw ur 2nd msg regarding the 87a and also read Sandy Meltzer's comments. I
>agree 100% with Sandy. In my earlier message I mentioned a few of the
>component failures I've had with Alpha products over the last 14 years.
>Nothing is perfect, but I would consider Alpha products and support to be
>exceptional. The 8877 and vacuum T/R relay that went "west"...
At the same time, no less. Hmmm.
>...on my 77dx
>approximately 33 months from date of purchase was replaced at "no charge".I
>didn't have to "haggle" with ETO about any "pro rated" credit amounts. ETO
>could have said the tube wasn't there problem and go away, but they
>didn't.
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.
- 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*.
Free, unsolicited advice for curious Alpha 87 and 88 owners: If you
experience sudden failure, it might be educational to pull the power
plug, remove the 3CX800A7s from the amplifier, and check them with a
current-limited high pot tester. Set the current limit for 100uA - if
there is an adjustment. Normal leakage is under 5uA at 5kV. In a
gold-sputtered 3CX800A7, with positive 5kV on the anode (negative on
grid), the leakage current is typically 50 or more uA. If the measured
leakage current decreases with reversed polarity, loose gold is
indicated. If the leakage current does not decrease with negative on
the anode, a leaky ceramic/metal seal is indicated.
Gold boils at 2966 degrees C. In my non-'expert' opinion, such
tempertures are quite unlikely to be caused by 14MHz SSB or CW.
R. L. Measures, 805-386-3734, AG6K
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