[GreenKeys] low current keying - 28

Wed Jan 29 19:58:39 EST 2014

Hi Guys and Gals,

I installed a 28ASR Dial TWX machine that had it's associated 101A  
data set separately mounted in a shielded case with approximately 48  
screws. This was at a location in Rolling Meadows, IL for the  
HALLICRAFTERS Company.  Because there are only so many characters you  
can code on the answer-back drum I coded it HALICFATERS which the  
company did not like.  It took them a day of meetings to decide how  
they wanted it coded.  I do not remember what it was but that was the  
first of several trips to their plant.

I had a SECRET clearance which is why it got the duty. There were only  
two of us in the shop so cleared.  I was always met by two government  
security guys and we followed a particular color (Red) in the tile  
floor to the room where they had the ASR, the data set and their  
KW-7.  Believe me it is hard to work with a man looking over each  
shoulder.  Anyway they kept calling trouble in that the TD would not  
start when the the KW-7 wanted it to start.  So I would have to remove  
the 48 screws and plug the amphenol connectors together to bypass the  
KW-7.  I would then dial up the 312-431-9167 ATL and show them that  
the ASR would do everything it was supposed to do. After that I would  
dial up the machine in our shop to exercise the TD.  I told them that  
the KW-7 was not providing a ground necessary to start the TD.... put  
the darn thing back together and reinstall the cover and the 48 screws  
and closed out the trouble with the dispatcher as trouble in the CPE  
(Customer Provided Equipment).

On the third or fourth visit I was getting upset with these so called  
engineers. So I asked them to look closely when they commanded the TD  
to start.  One of the men put his nose close to the TD and I used a  
BELL KS screwdriver to provide the necessary ground... the resultant  
arc caused the man to fall over backwards.  I never had another case  
of trouble at Hallicrafters.

Ye Old Teletype Repairman Don
K9TTY
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On 29 Jan 2014, at 5:04 PM, Duncan Brown wrote:

Nick,

In the 1960, the standard US Army TTY Crypto units were the KW-7 &  
KW-26. They were both unipolar.  The keyboard & tape reader Mark &  
Common connections ran directly to the Crypto box through a shielded  
cable and a mil  connector (don't remember the type, but I think it  
had 6-7 contacts; Selector magnet had a similar cable.) The Crypto box  
supplied a 50ua TX current loop (don't remember what the open-circuit  
voltage was).  At 50ua, 4.7K would only drop about 1/4 volt, and the  
two resistors & cap looks like a spark suppression circuit.  At 50ua,  
I don't think it would make much of a spark, but maybe they felt it  
was needed!

Or it could have been some weird ham mod!

The AN/GRC-46B RTTY system had a small switch box (SA-1243/GRC) in the  
cable between the TT-76 reperf TX line and the KW-7. It just had one  
(lockable) switch that was labeled "Open on Security Equipment  
Installed."  There was a 27K resistor across the switch which was  
switched out of the line when crypto equipment was removed to allow it  
to operate on a 20ma loop.

This was kind of a kluge and you would think if it was a low-level  
current limiting resistor, it would have been in the KW-7.  But it may  
have been for something like your M28 4.7K resistors.  I do not  
remember an external TX line resistor in other TT-76/KW-7 installations.

Have fun,

Duncan
K2OEQ

On 28-Jan-14 22:39, Nick England wrote:
> In getting a 28KTR working, I replaced some stuff inside the code
> generator - 4.7k ohm resistors in series with both mark and common
> leads and then a 0.01 uf cap across the line.
> The replacement shielded line from the code generator had an MS3101
> military connector on it, but this definitely didn't look like a
> factory or military change - the little circuit board that carried the
> resistors inside the code generator box was a piece of bakelite cut
> from some other terminal board to fit, and the clamp that held cable
> shield was also home-brew. The LPR selector magnets had a similar
> MS3101 military connector on a short length of  shielded cable.
>
> I rewired both code generator and selector magnets back to the
> original configuration, but I was wondering what this mod could be in
> aid of. So, not military low-level which is bipolar +/-6v, because
> only the marking contact was hooked up. And while it wasn't a
> military, factory, or WE modification, I can't figure out who would
> need to do such a thing. I'm puzzled (as usual). Any guesses?
>
> Cheers..
> Nick England K4NYW
> www.navy-radio.com
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