[GreenKeys] Teletype Part Numbers

[Jim Haynes]

On Wed, 9 Dec 2020, Jim Cooper wrote:

> On 9 Dec 2020 at 21:55, ad7i wrote:
>
>> I've never understood the concept of
>> the pulling and holding magnets for the
>> M15.
>
> Here's a simple explanation.
>
And according to the late Walt Zenner who invented the holding selector,
the real reason for it was so they could operate a loop with only 48 
volts.  It was a safety issue since the loop voltage is exposed on the
switchboard plugs in the original manual TWX system.