The AM Forum

I scored a 51J2 at the local swap on Sunday. Any thing special about this one I should know about?
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John N8QPC

Al Parker has some interesting articles documenting restorations of R-388s and a 51J4. Perhaps that will help.

http://www.boatanchors.org/

Joe Connor

  Hey John,

     No antenna/Break in relay like the R388 that has a relay
but you need to supply external power to it. (28VDc I Think)
Other than that it looks almost like a 388 which is a pretty
sweet RX. Congrats on scoring that!

73

/Dan

The R388 and the 51J look similar, but inside they are quite different....

 I finally got time to play with the receiver yesterday. Someone has recapped it but the sensitivity seems low. Time to test the tubes for starters, and go through the alignment. Luckily it came with the book. I was surprised too see how pricey this receiver was when new.

John

Relay needs 12VDC. I just finished wiring mute on my R388/URR.

John, check out the article I linked to. If I remember correctly, there is one mica cap that is notorious for going leaky and causing low sensitivity.

I read the article thanks.

A few mechanical things.

I like to clean the rear cams with some solvent and a Qtip, then I re-lube with silicone grease. Never gums and lasts forever, thin shmeer is all you need.

I also cleaned and lubed, gently all the sliding metal on metal parts

I relube all the rotating shaft bearings with 100 grade silicone oil, from the hobby shop that sells the stuff in 3oz bottles for RC cars shocks!

Especially lube the ant trimmer shaft!

Mine is smooth as silk now when you move a knob.

Soft tubes will cause low sensitivity. I just got a second R-388 and it had a soft tube in the IF, and was fairly deaf as a result.

Afaik, the 51J-3 and the R-388 are identical.

Watch out for the main plug in power supply cap - it can become leaky and make ur power transformer run very hot. I rebuilt mine with an octal plug, some aluminum tubing and filled it with modern caps and silicone rubber, put a cap on the end.

Fwiw, I use a dow-key type relay with a Valiant II (3 x 6146) running about 75w of carrier, and I do not mute the receiver, the isolation of the dow-key is sufficient to put the signal into the receiver at about 20dB over S9 (not that the meter shows an S9) and I simply use it for monitoring as I speak... I do have the speaker at sufficient distance and placement (and phase - it matters)  so as to not feed back. FYI.

I think the 51J-2 is slightly different inside...

I'm very happy with mine on AM. Use it all the time.

Considered a product detector mod, but never pulled the trigger. Think I'd try the 7360 tube first. There is a plug-in solid state thing being sold online. There are numerous other product detector mods in the mags from back in the day. Of course they switch in and out...

Totally classic receiver, top of the food chain! :D


           _-_-bear


the image is the one I just got, as it sits... love to see a pic of yours! :)

I finally got my computer to recognize my camera. I am not a big fan of windows 7. Any how here is a crappy picture of my 51J2.

Love the freq it's on in the pic....   :-)

--Shane
KD6VXI

Bear,

The pix you labeled "51J2" is NOT a J2...   It's an R-388, sometimes referred to as the 51J3...   Different meter and has the "ant trim" feature plus other changes underneath.    

Then there was the R388A with the added 3 mech. filter mod. That receiver is also called the 51J4

The pix poster by Detroit47 is, in fact, a 51J as noted on the bezel label... Not built to Gov. Spec....

He labeled his picture R-388:

(http://amfone.net/Amforum/index.php?action=dlattach;topic=37206.0;attach=44983;image)
R-388-BALLSTON.jpg (233.99 KB, 1480x1110 - viewed 24 times.)

Congrats on the 51J-2 Detroit47.  They only made about 1000 I believe.  I think the military designation was R-381.  This receiver was built in the 1950 / 1951 time frame.  They cost about $875 new which was a lot back then.  Enjoy!

It seems to me that someone removed the Collins emblem off the face of my receiver at the top. I doubt if i will ever be able to replace it. I wonder if there are reproductions around?

John N8QPC

http://www.ebay.com/sch/i.html?_nkw=collins%20emblem&clk_rvr_id=724745226097&adpos=1t2&MT_ID=70&crlp=15088291371_2416792&device=c&geo_id=10232&keyword=collins+emblem&crdt=0

http://www.advanced-optics.com/collins.htm

I have a 51J4 just two quick notes. One back in 1969 HR magazine there is a good article on rebuilding  the pto and setting the end points. These set it's a bit more work than the R-390 and it requires a special tool to loosen the lock ring to adjust the end points. Two rather than building a product detector I found just increasing the coupling from the bfo output does wonders. Best I remember the original was about 5 mmfd I increased it to 35mmfd. Really helped out a lot with ssb reception.
GL w/it
Terry N3GTE

It may be that yours was a military radio? Does it have 4 screw holes? Probably military then. Many of these seem to have had the tags removed.

Just a thought...

Btw, Ralph, I missed out on an auction for that 3 filter module on epay a few years back. Passed on it because it was in Australia and expected the shipping to be insane. Chatted with the seller and he related that the shipping would not have been very high... oh well.

Not sure I want mechanical filters at this point, although I do have a nice 500kc. AM filter, nice width (not too narrow)... :D

                   _-_-

    A scan of my nomenclature tag for an R-388 is here...

http://amfone.net/Amforum/index.php?topic=26335.msg199820#msg199820



/Dan

I guess I should have looked on Epay first. Thanks for the heads up. Also there are no holes for a tag.