[GreenKeys] Teletype Monopulse printer

[John Nagle]

> From: "Duncan M. Brown" <duncanancy at earthlink.net>
> Subject: Re: [GreenKeys] Teletype Monopulse printer
> To: "David Ross" <ross at hypertools.com>
> 
> Officially known as the "Model 36", the "Monopulse" sends one pulse for
> each character.  The length of the pulse controls how far the typewheel
> rotates.
> 
> I have never seen one, but I belive that the M36 typewheel is a cylinder
> like the type wheel on a M28 and TT-76 reperfs.  The M31 type surface is
> curved, but is only about 1/4 (or less?) of a full cylinder. 
> 
> The AWA Museum has a M36 transmitter.  It is about 4" square, with the
> letters of the alphabet arranged in a circle.  When you press a key, a
> rotating arm is released from its "rest" position and rotates to the key
> that was pressed.  During this rotation time, current flows and the
> receiver type wheel rotates also to the proper position.  Then, somehow,
> the transmitter rotating arm must return to the rest position before the
> next key is pressed.  We don't have a receiver (or if we do, I've never
> seen it) so I have never seen the whole system in operation.
> 
> They were designed for low speed, low volume, low cost applications, such
> as inter plant communications.  But I don't think that they ever became
> very popular.

>>
>> Brooke Clarke wrote:
>>> Hi:
>>>
>>> I've received the printer and have some photos at:
>>> http://www.prc68.com/I/Monopulse.shtml
>>> Unfortunately it's missing the print wheel and some unknown component
> that had 
>>> 3 wires cut.

     It's too bad you don't have the typewheel. That's going to be tough to
replace.  Otherwise you two could get together and hook up your transmitter and
receiver.

     It's interesting that Teletype built that thing.  It's similar to
some 19th century printing telegraph designs, like the Phelps
printing telegraph. ("http://www.telegraph-history.org/george-m-phelps/")
The early printing telegraphs had trouble staying in sync, but for the
Teletype 36, they seem to have assumed that both ends were running from
the same synchronous AC line, so the sync problem wasn't too hard.

     It's surprising, in a way, that Baudot teletype machines were
developed at all.  The continuously spinning typewheel and hammer
machines got up to 60WPM in the 1890s, but they were always "fussy"
about sync.  If someone had figured out phase-locked loops by
1930, we might have had, instead of mechanical Teletypes, better
spinning-wheel machines synchronized by PLLs implemented with
thyatrons.  The parts count and mechanical complexity of
the spinning wheel machines is far lower than the Baudot machines.
Something like that appeared around 1970 as the UNIVAC
DTC 300, a page printer with one big typewheel that moved across
the page while a printer hammer behind the paper fired at the
appropriate time.

    (Completely mechanical phased-locked loop flyball governors using
magnetic drag brakes could have been built as unison devices as
early as 1875 or so, when Edison was still designing stock tickers.
But nobody had the math for PLLs back then.  Also, cutting the bevel
gears for a differential was tough before milling machines.)

				John Nagle