1) Make sure you have the manual - I will refer mostly to Page 13
2) Power Off, unplugged, ALL cables disconnected - check continuity with a
VOM between Center pin of J4 and J5 - if you have continuity (roughly 0.2
ohm) you need to keep looking, if you do not, then then the problem should
be easy to trace down.
3) Assuming no continuity...
4) Power Off, unplugged, ALL cables disconnected, open it up and look at
J4, J5 and K4 for obvious issues - wires broken, burned, bad solder job from
a replacement made by some prior owner, etc. Chances are that it will be
immediately apparent what has happened and you can fix it in a
straightforward manner. For example, if the relay looks fried, replace it;
if one of the wires going to one of the connectors has come loose, repair
it.
5) If you have connectivity, then it isn't the amp; OR it is a problem that
is causing DC to go thru and RF not to go thru which, given the design,
seems unlikely. If it isn't the amp, try running the radio direct into the
antenna completely bypassing the amplifier - no cables touching the amp. If
that does not work for you then there is a problem at the antenna, the radio
or one of the cables you are using.
6) From what you have said, no continuity when off, no amplification when
on, relay appears to operate, it appears RF is discontinuous either at one
of J4 or J5 or at the connection to A or B of the K4 or at the jumper on the
K4 between the two normally open contacts. Most likely, as you suggest, one
of the wires has come loose - probably from a bad repair job in the distant
past - these amps were designed in the 70s and sold until the late 80s or
so. They were extremely well made for their day.
As to the RCA connectors - that was the thing at the time. Every high end
station had a Collins or a Drake and they all used RCA connectors for
carrying 100W level RF. Alpha wasn't trying to save a buck - they just
wanted happy customers. Nothing wrong with the RCA except it can come loose
easily and cause trouble. On my 78s I have replaced the RCA input connector
with an SO239 and I prefer that. I used a punch/die cutter (Greenly),
centered the tool with the existing hole and made a slightly bigger hole for
the SO239 (Don't drill it!!!). Install the new SO239 and you are done.
Just need to be neat. There is plenty of room to do this.
If you wind up replacing the K4 relay, understand that there are many
versions of the W88 relay. You want one that will preferably mount in the
same holes and use the same voltage and have the same specs. (Or you can go
crazy and install a pair of 26V RJ1A vacuum relays). The manual just calls
it a W-88 Magnecraft. eBay has many for sale in the $10 - $20 range. But
this one (shown in last schematic in manual lower right quadrant) is a DPDT
(6 contact (+ coil) - 2 circuit) 28 volt DC relay.
If you need a copy of the manual let me know.
D
David B. Ritchie, W6DR
dbritchie@gmail.com
+1-650-862-6400
-----Original Message-----
From: Amps <amps-bounces@contesting.com> On Behalf Of
amps-request@contesting.com
Sent: Saturday, April 15, 2023 9:00 AM
To: amps@contesting.com
Subject: Amps Digest, Vol 244, Issue 9
Send Amps mailing list submissions to
amps@contesting.com
To subscribe or unsubscribe via the World Wide Web, visit
http://lists.contesting.com/mailman/listinfo/amps
or, via email, send a message with subject or body 'help' to
amps-request@contesting.com
You can reach the person managing the list at
amps-owner@contesting.com
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Amps digest..."
Today's Topics:
1. ETO/Alpha 76 Tri-tube (Kathy Bookmiller)
----------------------------------------------------------------------
Message: 1
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
Message-ID: <1458331603.2075412.1681572797874@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8
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.
------------------------------
Subject: Digest Footer
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
------------------------------
End of Amps Digest, Vol 244, Issue 9
************************************
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|