[Amps] Alpha 87A reliability problem

[Phil Clements]

Happy New Year, Rag, and all the AMPS gang!

I have been running an Ameritron QSK-5 for many years
with no problems. No experience here with the Alphas.

I followed the instructions in the manual, and advice from
several PIN diode users, and I think that has made the
difference. The advice given today here on the reflector
was sage about being extra careful with ungrounded and
un-bled antennas, especially the longer wire antennas like my
40 meter double-extended Zep. You don't need a storm to
develop very high voltages on these things.

A few years back, in either CQ or QST, there was an article on
a HB PIN diode QSK box. (sorry--I forgot to save it) In recent
years, more robust diodes have become available than those
used by Alpha and Ameritron. I called Ameritron a couple of
years ago to see if they had plans to upgrade to the larger units,
but they said no; that they have had very few reported failures
on the QSK-5 boxes, and will stay with the present components.
Perhaps one of our readers has the make/model on the newer
diodes.

Rich is very correct, if you are into the digital modes including
high-speed keyboard CW, you will need the speed of the PIN
switch.

GL in solving your problem...

(((73)))
Phil, K5PC


> >My otherwise excellent 87A is too often out of service due to PIN-diodes
> >breaking down.
> >
> >Has somebody ever made a modification with vacuum relays instead ?
> >
> I have not, Rag, but this seems like a good idea since PIN diodes are
> easily shorted by lightning and by high SWR.  However, for >40wpm CW,
> relays are not fast enough.  Modifying with high-speed relays also
> presents an opportunity to remove the  RF-actuated T/R switching and use
> a transceiver-actuated electronic cathode bias switch (ECBS).  This will
> result in the bias switching always being in perfect sync with the RF
> switching, which will stop the tubes from being switched in and out of
> linear bias in the middle of soft-syllables and making rough-sounding
> audio.