[GreenKeys] Starting Up an Old Debate

[Bob Camp]

Hi

In this day and age of hyper protection on everything it's a little 
hard to imagine an environment that went from exposed 120 VDC to 
exposed 48 VDC on the basis of safety. I'm sure they did exactly that, 
it's just pretty far from the current state of affairs .....

If you do get a chance to scan in the magnet design notebook that would 
be great. I'm kind of revisiting the whole selector magnet thing (as 
you might have noticed ...).

	Thanks!

		Bob Camp
		KB8TQ


On May 31, 2004, at 1:02 PM, jhhaynes at earthlink.net wrote:

> There's nothing wrong with the saturation idea; we just don't know if
> Teletype used it.  When the core goes into saturation the incremental
> inductance collapses; but the strength of the magnet is no less than
> it was at the onset of saturation.
>
> According to Walt Zenner, who got the patent on it, the original reason
> for the holding magnet selector was th reduce the voltage on the cord
> circuits in the TWX switchboards.  With the earlier machines they were
> using 120V on the switchboard cords, where it is exposed to the 
> operators'
> hands and can be deadly.  So the holding magnet selector allowed them
> to run 48V on the cords.  That still seems pretty high, but was no
> higher than the voltage on telephone switchboard cords.
>
> I've just received a notebook on magnet design that belonged to some
> early Teletype engineer.  I'll scan it and add it to the Teletype
> Scrapbook CD ROM, and maybe will send out some individual page scans
> on the list.
>
>
>
> -- 
>
> jhhaynes at earthlink dot net
>
>