TELEX machine, modems

From: gil smith <>
Date: Fri Feb 21 18:22:01 2003

Hi George:

Most Model 32 machines seem to be Telex units; they have a rotary dialer
and four buttons at the front -- but the dialer is not for telephone
numbers (as it is on model 33 TWX machines which can have either a
rotary-dialer or touch-tone-dialer). Telex machines do not communicate
with modem frequencies, but use a speciallized DC signalling scheme,
described below. However, you can drive the unit with a standard current
loop interface. I can put you in touch with someone who has done this, if
you'd like.

If you do not have a dialer, but instead have a blank panel on the right
side (CCU), you have a "private-wire" machine, which is for a simple 20- or
60-mA current loop.

The M32 and M33 are based on the same crappy design, which was targeted for
low-use/low-cost applications, (as opposed to almost every other teletype
model, with bullet-proof parts for 24/7 operation). But I digress.

M32: 5-bit baudot (1-start/2-stop?), 50-baud, ~ $0 to $50
M33: 8-bit ascii (1-start/2-stop/even-parity), 110-baud, ~ $100 to $1200

According to my manual the telex CCU is for what they called
"Circuit-Switching-Service," and the buttons are labelled: START, DIAL,
LOCAL, and CONN(STOP), or possibly labelled: REQUEST, CONN, LCL, and
DISCONN. As I understand it, Telex is a dialup service that uses DC
signaling (no modem) and is 50-baud baudot. Telex was a service Western
Union brought to the US starting in 1958, after it had been used in Europe
for a long time -- the 50-baud was a European standard. I belive that Telex
machines had some sort of line-interface box (not a modem like an M33 twx)
in the stand.

Here's part of the manual description of the four-button
"Circuit-Switching" (Telex) CCU: "The dialer is a conventional telephone
type...contacts open and close to send dialing the idle
condition, there is a positive current of 0.005 ampere in the telegraph
loop. When the calling station operator depresses the START button, it
causes the shunting of a major portion of the loop resistance, and the loop
current increases to 0.060 ampere. The START button must be held while
switching apparatus in the telegraph exchange is made available. When the
circuit is ready, the telegraph exchange interrupts the 0.060 ampere loop
current for about 0.025 second. This "proceed-to-dial" signal causes the
DIAL lamp to illuminate at the calling station, and it locks the shunt to
the loop resistance so that the operator may release the START button and
proceed to dial the number of the called station...When dialing is
complete, the exchange furnishes the connection and signifies this by
reversing the telegraph loop current from positive to negative, which
causes the typing unit motor to start and the CONN light to illuminate.
Message transmission can now be exchanged between the connected
teletypewriters. The line signals are 0.060 ampere marking and zero current


>From: "George R. Gonzalez" <>
>Hi, I have just bought a nice clean TELEX machine, it's a TTY-32, 5-level
>with what looks like a phone line hookup, dial-type phone.
>I wonder if anybody knows what the modem standard is for this, and/or any
>phone number I could call to test this thingy out!

; vaux electronics, inc. 480-354-5556
; (fax: 480-354-5558)
Received on Fri Feb 21 2003 - 18:22:01 GMT

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