I have an Alpha 86. It's been a fantastic amp, literally loafing at
1500 watts output with headroom to spare. For like 20 years. But now it
is soft-FAULTing on transmit. I am pretty sure it's the diodes, because
I think it did not protect itself quite enough when I was doing some
boneheaded antenna adjustments on 160 meters. I'm pretty sure what
actually failed is the protection circuitry itself because that was not
the first time I had beat on that amp.
For comparison I have also had the failure N6TV describes - the fuse is
an easy fix, and the difference in the symptoms is you don't get the
FAULT light when the little fuse blows.
I have a paper around here somewhere that a fellow wrote that describes
in great detail how to convert our amps from PIN diodes to vacuum
relays. I am considering doing that, since QSK has fallen out of
fashion at N5OT and vacuum relays would be fine. It's funny to hear guys
say "I don't mind the noise of the vacuum relays." How things change!
They used to be the epitome of silence. But yeah, PIN diodes make less
sound than vacuum relays.
I think there may be a professional amp repair-modification person on
this reflector who does this exact modification. I can't remember who
it is. I wanna say "N4-something."
Cloud of Wisdom - can you remind me where to find this paper, and who
the amp repair person is? Chris might like to know it, and I would
benefit from being reminded.
Great amp. Too bad the tube isn't more popular or plentiful, but mine
are original, strong, and are only being limited by the fault protection
at the moment (which may be why they have lasted so long already!).
73 - Mark N5OT
On 8/7/2020 6:11 AM, Chris Wilson wrote:
I have an Alpha 86 here with suspected TX / RX switching pin diode
failure. The amps TUNE function is suspect, and switching between
standby and operate gives a vey attenuated RX signal in standby mode.
In TX it seems to operate, TUNE display aside, normally.
The manual's schematic shows them as stud mounted UM4001CR devices. I
am unable to source these, does anyone know of a current source for
them please? Alternatively does anyone have instructions for
conversion to using two vac relays? Fast CW is not required, and the
noise of the vac relays not really a concern. Thanks.
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