[Amps] UM4001CR pin diode source - or Alpha 86 vac relay mad

[Mark - N5OT]

Hi Chris,

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:
>
>    07/08/2020 12:07
>
> 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.
>