TELEX machine, modems

From: gil smith <>
Date: Sat Feb 22 12:37:00 2003

Hi Bruce:

When you say that the telex machines used a "high-voltage DC, 60mA current
loop," is that implying a 120V loop as in standard TTYs? The reason I ask
is that the "private-wire" current loop for an M32/33 is a max of something
like 45 volts on the loop supply. I presume then, that the telex interface
box was designed for the HV, 60-mil telex loop, and then in turn drove the
internal 20-mil input to the selector-magnet-driver card of the M32. Was
this telex interface box in the M32 stand?

I had not heard of later M32s having Telex Line Adapters for FSK modem
application. How can you identify which interface an M32 has? Was there a
different dialer CCU, like the one with six pushbuttons used on the twx 33s?

I have some additional telex info from other folks added below.

ps: Bruce, did you see the post about all those TTY machines for free in
Seattle? Lots of good stuff headed for the dump.


More telex info from George Hutchison:

Using a Teletype Corporation equipped telex machine on RTTY is relatively

You need a loop supply with a current limiting resistor (2K or so
wirewound pot) a double-pole double-throw switch, and the telex machine.

Connect the DPDT switch in the standard manner for reversing polarity.
Feed the loop supply (Such as one would find in a 28 LESU) through the pot
to the center terminals of the switch.

Wire the reversing terminals of the switch to the telex machine input

If you plug the telex machine into 110 VAC, with the loop supply
de-energized, it will run open. Some folks tweek the dial on the telex a
bit to get the machine to lock up, but this is not necessary.

Energize the loop supply. Depending upon the position of the DPDT Switch,
the machine will either stop running open, remain on and be ready to type
uponst, or will shutdown and the motor will stop. Flipping the switch will
result in the opposite condition to occur. With the machine energized and
the loop locked, set the loop current for 60 ma.

When the machine is on and ready to type, it will key the loop that is
coming from the loop supply. From there it is easy to use it to key
another machine, a transmitter, or what have you.

When the machine is in the off condition, motor shutdown, etc, depressing
the "LOCAL" button on the telex will cause it to come to life so you can
type locally.

I have an ST-6 that I removed the 110VAC that goes through the motor
control relay, and set it up with the reversing arrangement as described.
Most ST-6 motor control relays were DPDT. The loop current from the ST-6
goes through the motor control/now reversing relay, so when the ST-6 says
turn on the motor, the loop current flips polarity and turns on the telex
machine. Such a deal.

Thought some of you might like this bit of info.


George, W7KSJ

More telex info from Don Robert House:

I have always just used the loop rather than tapping into the SMD
circuitry. I set a loop supply of 120-130 vdc to 62.5 milliamps with
two machines wired in series into the loop. The machines usually
have a mounting cord on them for this purpose.

The M32, if it is a former Telex, it uses the ITA2 version of Baudot
code. It is a 7.00 unit code with 1 start bit and 1 stop bit, which
is 50 baud and 67 words per minute.

More telex info from Jim Haynes:

There are two Telex interfaces to the M32. One is neutral, and the
other is a polar adapter that plugs into the neutral one.

Look in the Western Union Technical Review CD ROM; I think it's all
documented in there.

And yes, it's 50 baud, 7.5 unit code.

More telex info from Wayne LeTourneau:

Most Telex's are 66 WPM, I have 60WPM gears in mine and I connect the local
loop to terminals 8 & 9 in the rear. Local loop set at 60ma and not to
exceed 100 VDC.

It copies fine, I'M using a Flesher 170 tu. It also has automatic caridge
return and automatic line feed, so can copy those RTTY stations that are
using computers and don't have enough sense to send a LF and CR at the
right time.
I cannot get mine to talk to itself yet, have not figured out how to get
the keyboard in series with the printer.
Actually, the selector Magnets on thease draw close to 500ma, so you have
to use the driver card, which is where terminals 8 & 9 end up.
Wayne WB0CTE


>From: "Bruce Lane" <>
> Now I'm glad I spent those years with Western Union's Field Service
division (when they still had one), fixing those things.
> The Model 32 Telex machine did not operate on a standard phone line. It
required a dedicated hookup to a specially-equipped Western Union central
office. The normal interface was high-voltage DC, 60mA current loop. In the
case of longer-than-typical cable pair length, a polar adapter was employed
to create a differential DC interface.
> The later Model 32's were equipped with TLA's (Telex Line Adapters) which
used FSK, as you've already guessed. I don't recall the frequencies
involved exactly, but 2200/2000Hz Mark/Space wants to stick in my head for
some reason.
> The Telex network, as far as I know, is long dead in the United States,
and some other of the more industrialized countries, replaced pretty much
by the Internet and FAXes. The Telex-ready Model 32's ran at around 67WPM
(Words per Minute)/50 baud. Amateur Radio RTTY standard calls for
60WPM/45.5 baud.
> In other words, you've got yourself a true museum piece there. You may be
able to, if you wanted, convert it for ham radio use. However, you would
need to change the motor gearing to bring the speed down a notch. Finding
the necessary gear would be an adventure at best, though I can suggest a
couple of possible sources if you want to try this.
> Enjoy!
>Bruce Lane, Owner & Head Hardware Heavy,
>Blue Feather Technologies --
>ARS KC7GR (Formerly WD6EOS) since 12-77 --

; vaux electronics, inc. 480-354-5556
; (fax: 480-354-5558)
Received on Sat Feb 22 2003 - 12:37:00 GMT

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