>> Tom--
>>
>> Thanks for the clarification. I was not at ETO during the 8877
>fiasco--but
>> I was experiencing the same issues with the 3CPX1500A7s used in our
>> 50 MHz wind profilers. Totally an EIMAC issue -- certainly not ETO's
>fault.
>
>The military had similar problems. It was not, as Rich tries to claim, a
>problem with specific amplifers.
>
Tom -- I did not say such. The 8877-heat dam problem lasted c, 13
months. Blaming Eimac for 8877 failures outside this period is NIH
syndrome. However, the problem of 8877 failures due to gold-sputtering
is amplifier-specific. The AL-1500 and the Alpha 77 have produced
humerous kaput 8877s with gold sputtering damage. [see Fig.24 on my Web
site; see "Parasitics Revisited" September 1990 *QST*]
>> Just a few years ago there was a problem with some 3CX800A7s. I kept
>> hearing from Eimac that we (while I was at Alpha/Power) were the only ones
>> having problems. Couldn't find any reason why ~30% of the new tubes
>> would fail within about 100 hours of use. They just got OLD very fast
>with low
>> emission and high grid current. Fortunately (or unfortunately--depending
>on
>> your perspective) K1FO at Lunar Link was having the same problem and we
>> started comparing notes. Steve did some excellent "CSI" detective work
>> and discovered that the tubes that would fail early would also put out
>full
>> output
>
>Ameritron was having the same problem during the same time period. Creeping
>high grid current and short life.
>
>The current problem is 3-500Z's
>
>> much better. But this issue persisted for more than a year--resulting
>> in Alpha amps working fine during their 48+ hour burn-in, but failing in
>the
>> field within weeks of being delivered.
>
>Don't feel bad. 100 572B amplifiers were sold, all with defective Svetlana
>572B's! Virtually 100% of the amplifiers failed.
>
I would like to autopsy some of these 572Bs.
>I fully expect tubes to get worse, not better, as older engineers retire
>coupled with a decreased demand making manufacturing a start and stop
>process. Tubes are on the way out, all the signs are there.
>
For AM broadcast service, 70-volt FETs and combiners seem to have taken
over.
later, Tom
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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