[HCARC] TTY's
Fred
cw4evr at hctc.net
Tue Jan 28 13:48:35 EST 2014
I keyed the 60 ma loop for the 15s and 19s with a ST-5 TU and a polar relay.
Quite a simple setup, the diagram is in Ham Notes, Ham Radio Magazine May
1974. I think I still have a manual for the stunt box set up, and may have
the BSP's out in the barn.
----- Original Message -----
From: "Virgil Bierschwale" <vbiersch at gmail.com>
To: "'John Canfield'" <bucket at janeandjohn.org>; <hcarc at mailman.qth.net>
Sent: Tuesday, January 28, 2014 12:06 PM
Subject: Re: [HCARC] TTY
>I hear you
>
> I'm wanting the model 28 for the reasons you described on the 33's and
> because of the offshoring stuff we have discussed.
>
> Consider it a statement that us ole ????s still have lots of miles left in
> us, that I hope to see in the news one of these days
>
> Virgil
> N5IVV
>
>
> -----Original Message-----
> From: hcarc-bounces at mailman.qth.net [mailto:hcarc-bounces at mailman.qth.net]
> On Behalf Of John Canfield
> Sent: Tuesday, January 28, 2014 12:00 PM
> To: hcarc at mailman.qth.net
> Subject: Re: [HCARC] TTY
>
> Good explanation from Kerry.
>
> When I worked for SW Bell in Austin, I was a Teletype tech for several
> years
> and worked on Models 28 to the Model 40. Fortunately the Models
> 15/19 were just phased out when I became a TTY tech. The Model 28
> selector
> magnets were 60 ma, the 33/35 were 20 ma. Model 37 & 40 were
> RS-232 and the 40/4 emulated IBM bisync terminals.
>
> Models up to and including the 28 were Baudot, the rest ASCII (except for
> the 40/4 which was EBCDIC.)
>
> The Model 33 was an inexpensive machine that was a nightmare to keep
> adjusted and running due to the design. To make adjustments, parts were
> designed to be bent (really!) instead of loosening a screw or nut/bolt on
> the 28/35/37 and then making the adjustment. The 33 keyboards were
> particularly horrible.
>
> I operated RTTY for many years with a 35ASR and I'm back on the air in
> digital modes with a couputer and couldn't be happier. The Teletypes were
> noisy, slow, and not particularly user friendly or easy to keep
> maintained.
>
> 73 de WB5THT <John>
> Harper
>
> On 1/28/2014 10:56 AM, SARA SANDSTROM wrote:
>> Teletype is a fascinating system. There were/are 2 basic interface
>> standards: 60 ma current loop and 20 ma current loop. The problem
>> with the 60 ma current loop is not the current. Most loop supplies
>> for the 60 ma standard provided 200 - 300 Volts. This was because of
>> the large inducta nce of the selector magnets in parallel. If you
>> didn't have enough voltage you couldn't drive the magnets. The 20 ma
>> standard was almost compatible with RS-232. You could use th e
>> approximately 12 Volts provided by a lot of RS-232 drivers to operate
>> the machines. As I understand it, the basic difference between a 60
>> ma machine and a 20 ma machine is the 60 ma machine had the selector
>> magnets in parallel while the 20 ma machine had them in series . By
>> the 70's most if not all military TTY gear for comm had been converted
>> to 20 ma low level operation. The TTY machines used as computer
>> terminals were probably never converted to low level but just
>> eventually replaced often by a selectr
> ic typewriter type terminal or a Texas Instrum ents termi nal called a
> "Silent 700 " which used heat sensitve paper, if I remember correctly .
>>
>> Even solid state TU's (terminal units) had no problem with the high level
> (60 ma) machines. At l east through the HAL ST-5000/ST- 6000 TU's , high
> level interfaces as well as low level, RS-232 and Mil Std 188c interfaces
> wereprovided . O ptical isolators were not required/used.
>>
>> Incidently, I believe one of our members, John Canfield, used to be an
> AT&T TTY guy .
>>
>> If you can still find one, most of the old terminal programs included
> Baudot as a choice and had no problem converting TTY signals to ASCII for
> internal computer use. The computer became a "Glass TTY". Works fine,
> very
> quiet, and doesn't smell of oil and dust! Many year s ago I got an Atari
> 800 computer for my son. I had a short program that converted a TTY
> signal
> to the ASCII. I used the Atari as my TTY terminal. A slow 8-bit
> processor
> had no problem keeping up with Baudot.
>>
>> Kerry
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>
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