[Collins] 51J-4

[Dr. Gerald N. Johnson]

The primary difference between a stock 51J-3 and 51J-4 is the mechanical 
filter module according to the Collins manuals. There were many J-3 made 
to mil spec a bit different than the civilian J-3.

I have a J-3 that appears to have started out life as a military model 
but the front panel is painted white, engraved as the factory did much 
of the time with a meatball emblem instead of the winged emblem or SN 
plate top center. I bought it from the estate of an ISU professor who 
taught radio courses and had many students go to work at Collins who 
also was the Iowa coordinator for Navy MARS for decades. I believe he 
got the panel from a student via Collins Surplus and changed the panel 
and he also changed the detector to a product detector and it has 
delayed AGC space wired in it. I'm pretty sure that in the factory in 
custom rack mounted test systems that Collins would repaint the panels 
to all match, hence the white paint, and probably the St. James smooth gray.

Its likely what you have was modified for a test stand or some other 
special application where the stock receiver only needed a bit of 
modification to fit in the task assigned.

And then a possible modification was to make if fit in a case and 
assembly of a competitors receiver as a retrofit or upgrade. There is 
some chance it was a very limited run, like one.

If someone on the CCA has a comment, please let us on the CRA list know 
what they have to say.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 11/18/2013 4:56 PM, KA9EGW wrote:
> Greetings to all!  New guy here; Brian KA9EGW since 1979.  I just acquired a
> rather odd 51J4 that has differences [besides the obvious mechanical
> filters] from my 51J-3:
>
> 1]  The panel, although appearing properly silkscreened, is gloss St. James
> Grey, not the usual sort-of-hammertone finish.
>
> 2]  No rack handle holes.
>
> 3]  Fuseholders [1 marked ‘spare’] in upper left panel corner.
>
> 4]  Only 3/16 [approx.] holes for rack mount screws, and only 2 per side.
>
> 5]  *No* input/output connections to front panel at all.  No headphone jack,
> no RTTY jack, no speaker jack, no DIODE LOAD tip jack…nothing.
>
> 6] Serial number is conspicuous by its absence, not stamped on rear panel
> like my J3.
>
> 7]  AUDIO OUT on rear is a funny little 3-pin job with female pins.
>
> 8]  POWER on rear panel is about a 10-pin or thereabouts with male pins.
>
> 9]  IF OUT is an RCA connector, riveted.  Looks OEM.
>
> 10]  No strain relief on line cord; it exits through about a ¼” hole.
>
> 11]  All 4 corners of the front panel are notched about 1/8” [V] x ½” [H].
>
> 12]  Lacks MFP stamps.  Lacks MFP yellowing too.
>
> 13]  It appears to lack nomenclature-plate mounting holes above the dial
> escutcheon, too.
>
> 14]  No model # engraved in dial escutcheon either.
>
> The meter movement looks the same as my 51J-3’s.  It has the same tool clips
> as my 51J-3.  The PTO s/n appears to be a handwritten “5903 CR”
>
> Please, what have I bought?
>
> 73, Brian KA9EGW
>
>
>