[GreenKeys] Model 28 signal lines

[Jim Cooper]

On 16 Oct 2019 at 23:00, ad7i wrote:

> Here's a link to a much more
> detailed version of the old
> electronic selector magnet driver. 

The 255A Polar Relay was an attempt to 
make the keying more sensitive than just 
using the machine's selector magnet ... 

A much smaller current could be used to 
control the input to the polar relay, and 
either polar keying or a bias on one winding 
and normal keying on the other winding allowed 
a lot of management of the timing and bias 
of the output contacts. 

In the early 1970s several companies began 
making Solid State polar relays ... Trepac was 
one, another by the Diamond Repeater Company 
(for whom I worked for several years... ) 

"old man" Bert Diamond was highly respected 
in the Teleprinter communications field at the time. 

Somewhere in storage I have a few of those 
solid state polar rleays too !!   and I know I have 
at least one 255A ... 

w2jc