[GreenKeys] Cashion Electronic ST6 converter

[Ralph Mowery]

Around 1980 I was just getting in to ham rtty.  Bought a model 19 from a
local ham that had a tube PAT  demodulator someone had built .  As by that
time most everything was narrow shift and retuning the TV horizontal coils
used in that converter worked, but not very well.   I built a version of the
ST-6 from the article in Ham Radio magazine.

 

The demodulator was built all on one perf board with point to point wiring
except the power supply.  I used the 741 chips except for the first one
(limiter) because I had them and it did cut down on the parts count .
Forgot what I used, but it was suppose to be much better than a 741 .  It
was not a 709.  Hoff said the 741 was not near as good as the 709 for the
limiter.  It worked very well as I spent many hours with it copying the pix
on 20 meters using a Heathkit SB101 for the receiver.  Then the pix tapes
were sent out over a 220 mhz repeater .

 

Ralph ku4pt

 

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Ralph Irish
Sent: Monday, July 01, 2019 9:56 PM
To: Jim Pruitt
Cc: GreenKeys at mailman.qth.net
Subject: Re: [GreenKeys] Cashion Electronic ST6 converter

 

Jim & Tom

 

A Navy MARS group took the ST-6 design and sort of 'modernized it'.  At the
time Hoff did the initial

design, the 741 chip was either non-existent or too expensive to consider
for the TU.

 

The 741 is a 'data-equalized' version of the 709 chip.  The 709 became
'data-equalized' by the addition

of four or five components at various parts of the chip's pins.  If you look
at the schematic, you will

see all but the front end 709 have much the same, if not identical set of
resistors and capacitors to

do this job.

 

The 741 was 'built that way' and didn't need the extra components.  So they
were used in all but the

'front end' of the TU.

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