[GreenKeys] Collins 709D-1 FSK keyer & 706A-1 TU

[Duncan Brown]

George,

Thanks for your comments on these Collins FSK units. You seem to be the 
only one to know about them.  Apparently Collins did not make many of 
the 706A-1 TUs, but if they were so much better than the URA-8, makes 
one wonder why.

Do you know anything about the 600 hz shift capability??

Thanks & 73,

Duncan
K2OEQ

On 02-Dec-14 04:34, Geo. Hutchison wrote:
> HIYA - - -
>
> Just got done looking at my copy of a 709D-1 Manual.
>
> Don't think they made very many of them.
>
> Date on my copy is Aug 23 1949.
>
> Collins part number is 520-9412-00
>
> I built a copy of one when I was in high school.
>
> Reggie Tibbets, W6ITH, had one in his Moraga, California Receiving 
> center, along with 51J4s, 51N-1 crystal controlled receivers, and 
> other exotic gear.
>
> He also had a pair of 706A-1 Terminal units, which were used in the 
> capacity of receiving all of the UPI news from Asia.
>
> He used two hand-picked frequencies of 14.595 and 15.537 megacycles. 
> Call signs were JAG-2 and JAP.
>
> Circuits were usually good for about 18 hours a day.
>
> He had about 400 acres of Rhombics and Sterba Curtain antennas for 
> this service.
>
> Unlike AP and others, who I believe leased circuits and receiving 
> facilities from Press Wireless, who fed the raw received signal (keyed 
> DC) to their bureaus, for editing and correction, ALL of the copy 
> picked up by the Tibbets facility which went to the UPI bureau in San 
> Fran was clean, ready to run copy.
>
> I built a copy of a 706A-1 when I was on the USS Aspro, AGSS-309, over 
> Christmas in 1961. The radio room was blown away by the quality of the 
> copy the 706A-1 turned out, which made the Navy URA-8A look like a 
> junk-box.
>
> There is no information anywhere on the 706A-1. When I was with 
> Rockwell-Collins we ran it through all of the archival libraries and 
> nothing was found.
>
> The two units Tibbets had were picked up by Collins representatives 
> shortly after Art Collins' death. (Art Collins and Reg Tibbets were 
> good buddies).
>
> The 706A-1 used  an input  bandpass filter centered on 2550 Cycles, 
> two 6AK5's as limiters, a discriminator circuit featuring two matched 
> audio transformers with  tuned filters (2125 and 2975 cycles) each to 
> one of a pair of of 6AL5's as detectors, and after a bit of DC 
> amplification drove a pair of 5686's as keyer tubes.
>
> Tuning the discriminators was a snap with the unit I built, as the 
> inductors used were a pair of UTC VIC series adjustable inductors 
> which could be tuned with an Allen Wrench. The band width of each 
> discriminator was controlled by using a slightly different value of 
> tuning capacitor for the mark and space channels. Feeding a tone and 
> using the Allen Wrench feature to set the tuning resulted in a system 
> which was fairly symmetrical in mark and space characteristics.
>
> 'Bout all I can tell anyone.
>
> W7TTY
>


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