STROWGER

I have reconstructed two small Strowger telephone exchanges. One of these is a simulator that allows two telephones to dial a number and connect to the other telephone. It has two subscriber circuits and one final selector. My other mini Strowger exchange connects four telephones. This exchange has two group selectors and two final selectors. The first caller uses the primary selectors. When the line is busy the next caller will be diverted to the secondary selectors.

For tone generation (dialtone, ringtone and occupied tone) I  either use an Arduino microcontroller or a genuine dynamotor. In the picture I have removed the cover of the camshaft of the dynamotor that controls the intermittent tone sequencing. The tones themselves and the 75V ringer signal are produced by an AC generator with special windings. The AC generator is driven by a 50V DC motor. 

Demo of my Strowger equipment