>
>hi Terry,
>
>There were some threads on that sometime back, but no specific
>remedies except that the '86 was just bypassed externally as I remember
>it.
>
>My Alpha has had all the latest mods, but the design still isn't
>"bullet proof". When I was in NDak recently, I was forced to
>operate low power in the ARRL 160 'test, when the '86 tripped out
>and destroyed one of the diodes. So now, I too am considering
>a system to replace the PIN diodes with a good quality vacuum
>relay and proper sequencing system so I can still have full QSK
>capabilities. I'll post any developments here.
// I found that a simple workaround to sequencing is Blazingly fast
relays -- i. e., use a relay speedup circuit to overcome the c. 0.3H in
the RJ1A - or HC1 - relay's coil. The circuit shown on Figure 7 of my
Web site makes the relays R/T T/R transistion in <2mS. Since the fastest
radio transitions in c. 5mS, hotswitching is obviated.
- C. 40% of the 86 and 87 owners that I have spoken with have had to
return them for factory repair. Sure, for faster than 40wpm CW/QSK, PIN
diodes are the only game in town -- however, PIN diodes are undoubtedly
more delicate and less forgiving than vacuum relays. For example, a RJ1A
will typically arc over at about 5x more voltage than a PIN diode. When
a PIN diode arcs, it's history/bye-bye/adios. When a vacuum relay arcs,
seldom fatal.
>
>Alpha had a "good" idea, but the design IMHO was not reliable.
>It was OK for the amplifier to "trip out" when the SWR got too high, but
>it shouldn't destroy itself in the process!!!
>
// Chortle. "There is no safety in unlimited technological hubris"
(McGeorge Bundy).
>I had asked Alpha for the schematics of the latest mods and was told
>that NO schematics were available. Can you imagine making
>several new circuit boards and not having any schematics?? BS!!
>
// Sure. GE's Medical division reportedly cancelled their MRI amp
contract with ETO because of similar taurine feculence and perceived
hubris. The all time hi-hi from Dick is his ARRL Handbook statement that
there has never been a parasitic in one of his amplifiers -- even though
he said he's seen c. 150 tubes with gold-sputtering leakage. (The
gold-sputtered 8874 in ''Parasitics Revisited'', Sept/Oct 1990 *QST* came
from an Alpha.)
cheers, Charlie
>On Thu, 27 Dec 2001 09:11:54 -0800 "Terry Gaiser" <w6ru@bak.rr.com>
>writes:
>> Has anybody replaced the PIN diode TR switching in the Alpha 86 with
>> relays? I would be very interested in seeing how you did it.
>>
>> Thanks Much,
>> Terry W6RU
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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