Collins 51J1 Help

[w***@gmail.com]

I'm working on a Collins 51J1. Originally came to me with a LOUD HUM but that was taken care of. Also had a very stiff band switch, resolved as well with some drops of machine lube (sewing machine oil). It's receiving on the first 3 lowest bands very well or those being the broadcast band and 2 above that confirmed. All other bands have a bit of noise but no reception and can receive the xtal calibrator signal when turned on.

Seeing as how I'm new to Collins receiver repair but not new to boat anchor and old radio repair, what could I do to fix the issue.

Thanks and 74 de,

Gary/N9VU

[Scott Dorsey]

I'm working on a Collins 51J1. Originally came to me with a LOUD HUM but t=
hat was taken care of. Also had a very stiff band switch, resolved as well=
with some drops of machine lube (sewing machine oil). It's receiving on t=
he first 3 lowest bands very well or those being the broadcast band and 2 a=
bove that confirmed. All other bands have a bit of noise but no reception =
and can receive the xtal calibrator signal when turned on. =20

The crystal calibrator injects directly into the 6AK5 front end tube, I
believe. So if you are heaving the crystal calibrator but not hearing a
signal generator plugged into the antenna jack, something is wrong between
the antenna jack and the 6AK5, which is likely to be the bandswitch
control or the tuned input networks.

Sit down with the signal generator and work out the actual input sensitivity
on the various bands, and write it down on paper. There are only six of
those tuned input networks for all the different bands and if one of them is
tuned right and the others are bad it will work on a couple bands but not
others. Also cramolin the hell out of that bandswitch, especially the first
three or four wafers.

Having all the sensitivities on paper will help a lot when you go to look
at the schematic and see which bands go through which paths.
--scott

Seeing as how I'm new to Collins receiver repair but not new to boat anchor=
and old radio repair, what could I do to fix the issue.
Thanks and 74 de,
Gary/N9VU

[Gary Bernstein]

Thanks Scott for the helpful reply. I'll check on those things. For what it's worth when I connect an antenna to the coax connector in the back of the radio (modification done by someone else), I hear some low grade radio noise which comes when connected, then disappears when disconnected. So from what I gather the receiver is doing what it should for the most part, but not on all bands. Your explanation makes sense. Time to bring out my HP signal generator (the pro model) and do some checks at this point. I am suspecting contacts to be the main issue. You'd have to hear the sound in person when I change bands. Not quiet a loud connection like on the first 3 bands, but it sounds like it's trying. That could be a good sign and not something major hopefully.

Again thank you for your help.

Gary

Post by Scott Dorsey

I'm working on a Collins 51J1. Originally came to me with a LOUD HUM but t=
hat was taken care of. Also had a very stiff band switch, resolved as well=
with some drops of machine lube (sewing machine oil). It's receiving on t=
he first 3 lowest bands very well or those being the broadcast band and 2 a=
bove that confirmed. All other bands have a bit of noise but no reception =
and can receive the xtal calibrator signal when turned on. =20

The crystal calibrator injects directly into the 6AK5 front end tube, I
believe. So if you are heaving the crystal calibrator but not hearing a
signal generator plugged into the antenna jack, something is wrong between
the antenna jack and the 6AK5, which is likely to be the bandswitch
control or the tuned input networks.
Sit down with the signal generator and work out the actual input sensitivity
on the various bands, and write it down on paper. There are only six of
those tuned input networks for all the different bands and if one of them is
tuned right and the others are bad it will work on a couple bands but not
others. Also cramolin the hell out of that bandswitch, especially the first
three or four wafers.
Having all the sensitivities on paper will help a lot when you go to look
at the schematic and see which bands go through which paths.
--scott

Seeing as how I'm new to Collins receiver repair but not new to boat anchor=
and old radio repair, what could I do to fix the issue.
Thanks and 74 de,
Gary/N9VU

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Thanks Scott for the helpful reply. I'll check on those things. For what =
it's worth when I connect an antenna to the coax connector in the back of t=
he radio (modification done by someone else), I hear some low grade radio n=
oise which comes when connected, then disappears when disconnected. So fro=
m what I gather the receiver is doing what it should for the most part, but=
not on all bands.

Be careful also, we're in a solar minimum. If you don't hear anything above
10 MHz, for instance, it's likely because there is nothing to hear. That is
why the signal generator is needed to know the real state of things.

Your explanation makes sense. Time to bring out my HP =
signal generator (the pro model) and do some checks at this point. I am sus=
pecting contacts to be the main issue. You'd have to hear the sound in per=
son when I change bands. Not quiet a loud connection like on the first 3 b=
ands, but it sounds like it's trying. That could be a good sign and not so=
mething major hopefully.

It's been more than thirty years since I worked on a 51J... I got mine working
great, and then traded it for an R-390A. I do miss the 51J tuning and the
better audio but the R-390 stability is amazing.
--scott