[Collins] 51J-5

[kirklandb at sympatico.ca]

Not sure what is meant by the pass band tuning working properly but I am guessing
they had "problems" because of the mixing arrangement in the 51J series.

Asides from bands 1-3, the 51J uses one crystal for every even/odd pair of bands.
This is done by using the PTO to on the low side of mixer frequency for one band, and on
the high side of the mixer for the other frequency.  This is why the KHz dial is calibrated in
both clockwise and counter clockwise directions.

As I recall from a 75A4, pass band tuning is done by literally mechanically shifting the PTO (ie. rotating it).
Obviously a shift of  +1KHz on one band will result in a shift of -1KHz it's paired band.  This is also 
what makes USB/LSB operation so much fun on the 51J series - you have to alternate the BFO position
between bands to stay at USB (or LSB).

Bands 2,3 of the 51j series use the PTO to directly mix with the incoming RF to get a 500 KHz IF.

Band 1, uses triple conversion.

> From: ckepus at comcast.net
> To: Collins at mailman.qth.net
> Date: Wed, 14 Apr 2010 00:54:43 -0700
> Subject: [Collins] 51J-5
> 
> For those of you who might be interested in the 51J-5.
> 
>  
> 
>  I sent a request to the Hammond Museum of Radio for info on the 51J-5 that
> they acquired.   Larry Asp, a museum volunteer, was kind enough to respond
> and also sent me three pictures.  However, they are not quite as nice as the
> three pictures of the 51J-5 on the Collins Radio Association site here:
> http://www.collinsra.com/cra_album/0009/cra_0009.html.  
> 
>  
> 
> Here are Larry's comments:
> 
>  
> 
> "Chris - I volunteer at the museum - here are photos of the 51J5. There may
> be only 2 in existence - I found out some information on one of them, we
> have #2, havnt found out the fate (if any) of the 3rd." 
> 
>  
> 
> ".. we have not turned it on yet. However it was in regular use by its
> former owner, and was aligned as little as 4 yrs ago, and was in working
> orderl  Since it is a prototype,  not all the bugs were worked out of it.
> The passband tuning works on only odd bands properly, realingning it
> differently, the pass band works only on even bands properly. Since the 51S1
> (newer technology) went into production instead, thats the way it was left.
> This radio was made in Canada in Collins Toronto plant where the last 75A4s
> were made. They were preparing a new model general coverage reciever. So -
> it has a 51J4 tuning and IF arrangment, and a 75A4 passband tuning,
> mechanical filters, and SSB detector. It is likely the mechanical filters
> are prototypes since the 51J4s use 500kc (I dont know how they modified the
> filters), and it is in a 75A4 case. We have no papers or diagrams of the
> radio, and it is not mentioned in any Collins books I have come accross.
> There is a write up done for the CCA about 10 yrs ago on the radio written
> by Peter Lower. For the moment it is on display beside a 75A4 in the
> museum's Collins collection. Picture(s) will go into the museums web site
> soon, and hopefully it will generate some interest and turn up more
> provenance for the piece. We would love to get hold of a diagram. We don't
> plan any full exams yet. We understand that another one of these turned up
> at Dayton several yrs ago for 2 or 3 yrs running - we dont know where it
> went. The museum is happy to have the piece so it can be appreciated by
> anyone who has an interest in Collins." 
> 
>  
> 
>  
> 
> 73,
> 
> Chris
> 
> W7JPG 
> 
>  
> 
>  
> 
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