Fair price and ways to find a teletype

Dave Wade dave.g4ugm at gmail.com
Fri Oct 16 02:47:28 CDT 2015

In Volume 1 Issue 6 August 1979 of the '68' Micro Journal I see there is a
routine to bit-bang 5-level code to a Teleprinter.....
.. I know that's late 70's but in the UK older 5-Level machines were
available cheaply as the GPO (General Post Office)
moved from older Creed-7's onto Creed 444's for its Telex and Telegram

I don't know what happened in the US but many Hams had Model 15 TTY's and I
would have thought they were available
at a reasonable cost , well certainly as compared to a Model 33. Note there
was also a model 32 which is 5-level version of the 33...

So yes they were used, but perhaps not as the only input device...

Dave Wade

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brad
> Sent: 16 October 2015 07:20
> To: 'General Discussion: On-Topic and Off-Topic Posts'
> <cctalk at classiccmp.org>
> Subject: RE: Fair price and ways to find a teletype
> Thanks for this great explanation.  So would anyone doing computing back
> the early 70s have used a 5 level machine?
> I saw this one on ebay (or is it two?  Not sure what the deal is here)
> probably sacked:
> http://www.ebay.com/itm/Teletype-equipment-1-model-28-writer-1-
> reperforater-
> 1-50vdc-supply-etc-
> /121784463105?hash=item1c5aeb6f01:g:UR8AAOSwnDZUJHWs
> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Brent
> Hilpert
> Sent: Thursday, October 15, 2015 10:07 PM
> To: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>
> Subject: Re: Fair price and ways to find a teletype
> On 2015-Oct-15, at 6:25 PM, Brad wrote:
> >
> > Also separate question to others:  I want to stay away from the Baudot
> machines, right?  (ie. Model 28, etc)
> I'd say it largely depends on what your interests or purposes are.
> A brief overview of the technology:
> In the main, there were 3 generations of teletypes:
> 	Era				Common Model	Code
> Speed		Common Interface		Mechanism
> 	======			============	==========
> =======	===============		============
> 1)	1930s-40s:		Model 15,19		5-level
> ~30-50 bps	60mA current loop		Modified Typewriter Cage
> 2)	1950s-60s:		Model 28		5-level
> <=75 bps	60mA current loop		Typebox
> 3)	1960s-70s:		Model 33		7/8-level/ASCII	110
> bps		20mA current loop		Type Cylinder
> These are the "page printers" that would type across and down sheet paper
> fed from a roll.
> There are other models, variations on the above.
> Not included here are the tape printers, simpler mechanisms that printed
> one dimension on a narrow paper tape, ala stock tickers.
> The mechanism was the overriding distinction between these generations as
> speed and code capability followed from the mechanism:
> 	1) Modified Typewriter Cage:
> 			Decoding bars select 1-of-30-odd symbol/type arms
> arrayed in an arc, to swing and hit the paper, just like a common
> 	2) Typebox:
> 			An ~ 1" by 2" metal box holds typeface symbol pins
> two 4*8 matrices.
> 			The box is shifted up/down and left/right to bring a
> selected
> 			symbol pin between a hammer and the paper.
> 	3) Type Cylinder:
> 			A cylinder embossed with the typeface is moved
> up/down and rotated CW/CCW to select a symbol.
> The 5-level devices are commonly referred to as Baudot devices but this is
> not strictly correct as they generally use the ITA2/USTTY codes
> Telegraphy Alphabet No.2).
> The speed of Model 28s (at least) was determined by a selected gear-set.
> 5-level machines need code conversion of course.
> They all need current loop interfaces.
> A lot of old computer equipment will do 110 bps as the 33s were so
> associated with computers.
> For working form modern equipment, the bit rates for all of them are
> potentially awkward.
> When working on the 28s, which were geared for 75 bps, I lucked out as I
> found the USB-serial interface I was using could do 75 bps
> - not entirely surprising as 75 is a factor of 2 down in the common
> 9600,1200,300 bps series. How many USB-serial interfaces are capable of
> I have no idea.
> Regardless, the baud rates are slow enough that bit-banging from a program
> is not difficult, or an adjustable RC oscillator to a UART should do.
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