Date: Sat, 15 Apr 2023 15:33:17 +0000 (UTC)
From: Kathy Bookmiller <wb2aio@yahoo.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: [Amps] ETO/Alpha 76 Tri-tube
Hello,I've slowly developed a problem with my amp after years of light use.
It appears to have had a failure in the antenna relay, or at least in its
conductivityon receive.My rig went dead the other day and I slowly started
looking over all my connecting cables and found a couple that are
suspect-gee, they were only built 60+ years ago for hooking up a SB10
converter to the Apachie transmitter back in the day:) But after changing
them out, the rig is still dead and I checked the conductivity between the
two in/out jacks and it is open. OK, no antenna, will make the rig sound
dead.
So it looks like the relay contact has failed, wire fell off, ?? I always
hated the way Alpha used an RCA/phono plug for the input, just a lousy way
to save a dollar over an SO239 IMHO, but up to now, no problem as when I
one time years ago looked at changing it to an SO239, I decided it was to
much work changing it for what I'd gain.
But now it is probably time to open it up and see what has opened up.I'm
asking if anyone else has had a similar failure and what they had to do to
correct it, if finding the fault won't show an obvious fix.
73,
Kathy, w2nkPS I did fire up the amp. and cycled the ant. relay a few times,
but no change. It also wouldn't 'amp' when given some drive, so suspect is
the input RCA plug, but that is just a guess at this point.
### Losing RX is typ an open NC contact. Typ the NC contact on the input
portion of the TR relay is wired over to the NC contact on the output
relay.
But if you can't drive the amp, the input relay is suspect.....or wiring
from RCA input jack to COM of the input portion of the TR relay. IF the
output relay was trashed, and drive applied, you would have 1.5 kw into a
wide open..and probably arc the load cap.
But u can't rx or tx..that leaves the RCA to COM of input relay a good
place to look 1st.
A 5/8" greenlee punch (and possibly a 9/16") will clear a SO-239 nicely.
They typ have a 1/4" draw stud. Being on the rear apron, you could
always remove the RCA jack, then ream out the hole to 5/8", using either a
step bit, or in 2 x stages, like a 3/8" bit, then a 5/8" bit. Then you
gotta mark the 4 x holes for the 4 x 6-32 SS machine screws.
Use a good SO-239, with the teflon.
RCA for an input ? wth ? Talk about cheap.
Jim VE7RF
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