Windows XD,

The circled item on the schematic is a polar relay and it plugged into the socket in your picture.  The polar relay was the opto-coupler of the 1930s.  It isolated the machine's loop from the line.  

When these machines were originally developed (in the 1900-1930s) they were used on telegraph lines that could be 20 miles (or more) long.  Teletype Corp. used the generic term "Printing Telegraph" for their equipment up into the 1950s.

Since our TTY loops are measured in feet, not miles, we don't need the polar "Line Relay" option any more (though a lot of the M28 equipment still used them).

We generally just wire the selector magnets in series with the keyboard into our local 60 ma current loop, which is generally supplied by the modem/Terminal Unit/FSK Converter.  just make sure that the loop is limited to 60 ma before connecting it to the M19!

So you can just bypass and forget about the polar Line Relay.

Good luck & Have fun,

Duncan
K2OEQ


-------- Forwarded Message --------
Subject: Re: [GreenKeys] Is this part this?
Date: Mon, 28 Jul 2025 11:02:27 -0400
From: Windows XD <[email protected]>
To: Duncan Brown <[email protected]>


Apologies, it's a model 19, the photos should be attached to this post.

On Mon, Jul 28, 2025, 9:20 AM Duncan Brown <[email protected]> wrote:
What model TTY??

On 7/28/2025 8:54 AM, John, W9DDD wrote:
Was there supposed to be attachments or a link?


On 7/27/2025 11:07 PM, Windows XD wrote:
Dear all,

I'm finally getting back to my teletype project, and mine seems all miswired. Is the circled part on the schematic the same part that's circled in the photo?

P.S. What is it? Is it something kind of transformer?

All help is appreciated!!


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Home: http://mailman.qth.net/mailman/listinfo/greenkeys
Help: http://mailman.qth.net/mmfaq.htm
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>>> Jordan Spencer Cunningham's GreenKeys Search Tool: https://teletype.net/gksearch
>>> 2002-to-present greenkeys archive: http://mailman.qth.net/pipermail/greenkeys/
>>> 1998-to-2001 greenkeys archive: http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.html

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
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