Workings of a TTY

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Tue Dec 2 05:58:06 1997

On Mon, 1 Dec 1997, Tim Shoppa wrote:
> I suspect that Riccardo was talking about non-Teletype-of-Skokie-Illinois
> equipment which had an entirely different adjustment procedure. I
> have no proof of this except for the fact that he's nowhere near
> Skokie Illinois :-) Several comments related to European power have
> led me to believe that 20-30 years ago, their power grid didn't necessarily
> have the rock-stable frequency characteristics that many of us in
> North America take for granted, so perhaps some European machines don't
> use synchronous motors with gear sets, but instead allow the speed to
> be adjusted. If someone familiar with European TTY's would educate me
> about exactly what Riccardo was talking about, I would greatly appreciate it!

Creed machines (both teleprinters and paper tape readers, etc) used
Commutator motors in many of there machines (certainly up to the 7E).
These had a mechanical governor on the end of the motor spindle - a
weighted spring that operated a pair of contacts when it was up to speed.
There's a large power resistor in parallel with the contacts.

AC machines tended to have series-wound motors with the governor in series
with the whole thing. This flavour has contacts that open when up to
speed. DC machines tended to have shunt wound motors with the governor in
series with the field only. The contacts closed (increasing the field
current) when up to speed to slow down the motor.

The Creed 444 has an induction motor of some kind, and I think no
governor. It's been a while since I opened the motor box in that machine,
though

I've seen an Olivetti TE300 which seemed to have a capacitor-run induction
motor with a governor on the spindle. I guess it was wired in series with
the entire motor - it certainly was not a simple starting contact since
there was as speed adjustment screw on it.

Adjusting Creeds is an entertainment. The spring tension screw is on the
governor itself - and it's connected to one of the contacts. Thus you
can't adjust it when running, and if you have any sense you pull out the
mains plug when tweaking it. Single-pole mains switches always end up in
the neutral wire by murphy's law, you see...

There's some info on this in the RSGB Teleprinter Handbook if you can find
a copy of that.

Hope the above helps.

> Tim.
>

-tony
Received on Tue Dec 02 1997 - 05:58:06 GMT