[SML] Telephone line simulator

[Kristi R-C]

My dad made one for a school play when I was in HS that I've used dozens of times. Simple hand crank to generate voltage to trigger the ringer. Old Ma Bell phone circa 1960 on the other end. 
Last time I used it was for a performance of Bugsy Malone I directed when I was still teaching. When I called for the cue, nothing happened. Called again - still nothing. ASM told me "He's turning the handle, but the wire's broken off!" I slid open the booth window from the back of the house and loudly yelled "Brrrrrring!  Brrrrrring!"  Audience laughed, 8th grade actor took his cue and the show went on.
God I miss those times... 
Kristi R-C


-----Original Message-----
From: Jerry Durand via Stagecraft <stagecraft at theatrical.net>
To: Stagecraft <stagecraft at theatrical.net>
Cc: Jerry Durand <jdurand at durandinterstellar.com>
Sent: Sat, Apr 11, 2020 1:03 am
Subject: Re: [SML] Telephone line simulator

For the low of budget people, if you just need to generate ring you can do so with bits you might have laying around.

You'll need:
An audio source for 20Hz sine wave, pulsed in whatever cadence you want.

An audio amplifier, I used a Radio Shack PA amplifier for one setup.  Doesn't need to be quality, just function.

If the amplifier has 70 volt line out, you can skip the transformer in the next line.

An 8 ohm to 70 volt PA transformer.

A blocking capacitor, steal a RUN capacitor from an induction motor you're not using.

The capacitor isn't strictly needed, but does limit current.

Circuit is audio source > amplifier > 8-transformer-70 > capacitor in series with one lead > telephone.

Be sure and cut the audio when the actor picks up, you don't want to blast his ear with the ring signal.  Maybe remove the speaker from the phone.

Experiment to find what works well with your phone and gear.



---
Jerry Durand, Durand Interstellar, Inc. +1 408 356-3886
www.DurandInterstellar.com & www.DurandInterstellar.ru


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