[GreenKeys] Rotary telephone switches?

[Harold Hallikainen]

On Sun, November 26, 2023 7:56 pm, Doug Alderdice via GreenKeys wrote:
> While step-by-step and other electro-mechanical methods of telephone
> switching are long gone from the PSTN, there are quite a number of
> hobbyists/collectors/nut cases who have small, or in some cases quite
> large, step-by-step "central offices" in their homes ... not unlike
> these guys I know who have old Teletypes running in their homes, ;)
>
> I happen to have a small SxS switch I built, but again there are a bunch
> of others who do, too, and some read this list.
>
> Whatcha got in the tools?
>
> Doug A.

I built a small step-by-step switch in my garage when in high school using
Strowger switches discarded by Pacific Telephone and Telegraph. I still
remember the A-relays, which were dual coil relays that would release when
going on hook or during dial pulses. One end of the dual coil went to
ground, the other to -48V, and the subscriber line went between the two
coils. The inductance was high enough that the AC voice voltage was
developed across the coils and sent to wipers on the switches to the
called phone. The B relay was a slow release relay that was used to
separate dial pulses from on-hook. Another relay (maybe C?). separated
dialed digits. I had a Sub-Cycle ring generator, a dial tone generator,
and motorized cam switches for ringing and busy cadence. Fun stuff!

A few years ago, I wrote documentation on the demonstration step switch in
the Telecom History Group museum in the Mountain States Telephone and
Telegraph company building in Denver. I also scanned some of the MTT
company newsletters ( https://bh.hallikainen.org/thg/monitor/ ).

My first step switch, which I built in Junior High, was made out of old
relays and steppers from a busted up pinball machine a friend found at the
dump.

Harold
https://w6iwi.org