Steve,

The polar relay was to isolate the local loop from the signal loop (which, in the land-line days, could be many miles long).  The polar relay also would clean up distortion on the signal line.

When operating a TTY from a FSK converter or modem, the polar relay is not needed and the TTY's selector magnet can be wired directly to the FSK converter's loop.

There may be times when operating multiple machines, that a polar relay is helpful, which is why most M28 machines still use them. 

In the US Army, c1950-80, the Kleinschmidt machines almost never used polar relays.

So don't worry about the polar relay socket, just wire the selector magnets into your loop (with sufficient resistance to set the loop current - typically 60 ma. for the M15).

Have fun,

Duncan Brown, K2OEQ
USASA    31J30

Antique Wireless Association
 Communication Technologies Museum
   Asst. Curator, Commercial Equipment
(also chief TTY op & repairman)

i-Telex: 212503

www.antiquewireless.org
AWA Youtube channel: https://www.youtube.com/channel/UCX55peBhzeX1qps_VYXdLBA





On 1/15/2025 1:06 PM, steve bennett via GreenKeys wrote:
John,

  In the video Mark mentions polar relay but he says it optional.
He does not explain.
When would you need to use it?

Thanks,
-Steve

On Wednesday, January 15, 2025 at 12:21:55 PM EST, John, W9DDD <[email protected]> wrote:


That is the bracket with socket for a line (polar) relay. Relay not there.


On 1/15/2025 10:51 AM, steve bennett via GreenKeys wrote:
GKs,

 What is the purpose of this relay shown in the Curious Mark video?
Inline image

-Steve


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-- 
---
----
The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]


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
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