[GreenKeys] Collins 709D-1 FSK keyer

[Geo. Hutchison]

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