[Amps] Re: Wierd Problem with Alpha 76PA

["WX5L" <wx5l@charter.net>]

Hello to the Amp group,

I have an mid 1980's Alpha 76PA amp which is working normal in the transmit
mode.

The problem arises in the receive mode  where I have noticed 2 to 3 S-unit
loss in receive signal. after unkeying the amp.

I am using a signal generator to produce a solid signal for testing.

I can push the SSB/CW switch into the OUT position and the signal
immediately returns to normal. I then push the SSB switch IN and just tap
the PTT switch of my microphone and notice the loss of signal on the
S-Meter. I can continue tapping the PTT switch of the mic and signal will
return to normal after several attempts.

My transceiver is a Yaesu FT-1000MP Mark V which has always been consistent
barefoot or with amp off. As a test I pulled out my second rig an Icom
IC-751A. The results were identical. Therefore the trouble is not with the
transceiver. I checked all coax connections and are OK.

The first thing I checked was the TX/RX relay K-4. Of course when the amp 
is
off the TX/RX is by-passing RF through K4 back out. As said before that has
never been a problem. Only after I key-up energizing K4 to transmit then
back to RX does the problem surface. While I had it opened up I burnished
and thoroughly cleaned K-4 but had no effect. I also burnished and cleaned
K-3 relay which is the plate voltage relay selecting SSB or CW. The reason 
I
cleaned K-3 was while in the diminished signal I can pop out the SSB button
to OUT and signal returns. Cleaning K-3 had no effect.

I would appreciate any comments or advice about this problem. What's really
confusing me is that in the receive mode K-4 should just be looping the
receive signal back out to the transceiver with no other interaction but
that's not the case. There is some interaction degrading the signal in the
RX.

While I was chasing VK0MT on 40 meters the other morning it made the
difference of copy and no copy for me. After each transmission I kept
tapping the mike PTT to regain full signal.

Please HELP!

Cheers,

Randy
WX5L

WX5L@charter.net
Thibodaux, Louisiana

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