[GreenKeys] M15

[Jack]

Ma Bell used 75 wpm for 15's on their internal Service Order network.
The function clutch spring had a yellow color code, otherwise
nothing else was changed. We had 15's and 14 TD's and 14 reperfs running
at 75 in the early 1970's in NY. some 28 RO's ran at 75 until they
were upgraded to 100 wpm then were replaced with 35 RO's at 110 Baud
and some Model 40's.

Jack K0TTY

NNNN



-----Original Message-----
From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Jim
Haynes
Sent: Monday, April 13, 2015 9:17 PM
To: COURYHOUSE at aol.com
Cc: Til128 at aol.com; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] M15


My understanding is that it was designed to go to 75 wpm.  Or maybe was
originally designed for 60 and then was found satisfactory at 75, perhaps
with a few changes.  What I don't know is who used them at that speed.
We know AP and UPI ran them at 60 wpm.  Seems like the wire services would
most benefit from the higher speed, except maybe they still into the 1940s
had some Model 12 machines in service.  TWX stayed at 60 wpm until the
cutover to dial TWX and 8-level machines.  A.P. went so far as to convert
their machines to 50 baud - I've wondered why they didn't go to 75 wpm
instead.  So it must have been largely private services that used 75 wpm.

We know that in WW-II the military made some use of 15s running at 100 wpm,
accepting the need for increased maintenance to get the higher traffic
capacity.  I would assume that was largely on land lines within CONUS, since
we never encounter old military machines from the field set up for 100 wpm.

Another large user of TTY equipment was the CAA/FAA and Weather Bureau, but
I believe they operated at 60 wpm until the cutover to ADIS about 1960.  By
then they had pretty much phased out the 15s in favor of 28s.

In message switching systems such as 81D1 it is desirable to operate the
cross-office circuits faster than the out station circuits, and the cross
office circuits could operate at 75 wpm, but there was no need for printers
on those circuits.

So who were the 75 wpm users?

On Mon, 13 Apr 2015, Ed Sharpe Archivist for SMECC via GreenKeys wrote:

> 75 wpm is  booking along   for a  15! It has a nice  sound!
> I rather  like it.... but     I wonder what the wear  factor is..?
>