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  • 1921 Westinghouse "Aeriola Senior."
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  • 1939 Silvertone 6256B
  • 1939(?) Radio Lamp Co. "Radio-Sight"
  • 1940 Philco 40-185
  • 1946 Motorola 65x11A
  • 1947 RCA Victor 65X1
  • 1947 Stewart Warner 9000B
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§ About the Project § Email Me §
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Self-Contained Rotary Dial and Electro-Mechanical Telephone Exchange Demonstrator.
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About The Project

Purpose:
To entertain and educate my grand kids.

What It Does:
It is a basic 3 digit telephone exchange that demonstrates, in a small way, how telephone calls were completed using rotary-dial telephones and electro-mechanical switching equipment that were in use from 1890's until the 1990's.
It allows the younger generation to learn how to dial a rotary dial telephone and appreciate the way telephone calls were completed before smart-phones.


Background:
My 35 year career with the phone company (GTE then Verizon), began in a step-by-step Central Office, filled with tens of thousands of Strowger Selectors and Connectors like seen above.(Also; Line-Finders, Directors, Translators, Ticketers, Register-Resenders etc. but that's another story).

Challenges:
To provide the following items that were normally supplied by the Central Office:
  • 50vdc power for the Strowger Switches.
  • 25 cycle ringing generator to ring the called telephone.
  • Office tones. (Dial tone, ring-back tone & busy tone)
  • Disconnected number announcement.
  • ​"Celebrity" numbers to call.

What Was Done:
  • To power the Strowger Step-By-Step switches, I constructed a 50vdc power supply using a step-down transformer and a “pi” section filter of 2 capacitors and a resistor. 
  • For the ringing generator, I built a 25 cycle power supply using a 555 timer chip and a door bell transformer used as a step up transformer.
  • ​For the office tones, I used three record/playback modules for the dial, ring-back & busy tones.  All are recorded with actual rotary-dial era Central Office tones for added realism.
  • Another record/playback module is used for the disconnected number recording..
  • The "Called Telephone" is provided with a 3 digit phone number, for answering calls.
  • ​Just for fun, I added more record/playback modules with the voices of Mickey Mouse, Darth Vader & Scooby Doo answering the telephone. Each with its own 3 digit phone number which automatically answers when dialed.
  • Unassigned phone numbers either go to Busy Tone or Disconnect Recording
  • One 3 digit phone number allows a caller to record their own message and then dial another number to play it back.
  • The "payphone motif" on the called telephone is just for whimsy.​
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