Previous cinematographer turned maker Thomas Burns has turned two Soviet-era rotary telephones into a place-to-position intercom system — employing a absolutely-analog circuit and a vintage 55V transformer able of placing out an amazing 250A.
“I required an intercom method for our family’s computer system maintenance business enterprise. We restore a whole lot of vintage tech at our store, so I made a decision to make this technique using two Soviet-manufactured rotary telephones from the 1980s,” Burns clarifies. “Modifying a pair of these telephones so that you can speak and listen is fairly easy: it in essence only needs around 15V of immediate existing, in addition a resistor. But finding the phones to ring is a little bit additional sophisticated, mainly because the ring circuit needs alternating latest.”
Customarily, turning vintage telephones into intercoms includes gutting the hardware and changing it with modern electronics. With two very well-saved telephones from the 1980s, however, performing so would have been a disappointment — so Burns turned to classic analog style to put collectively an intercom circuit which would use the phones’ present ringers, leading to 1 to audio when the handset of the other is picked up.
“I developed this circuit dependent on some aged schematics that have been floating all around Russian-talking electronics circles for a long time,” Burns points out. “The concept is this: when a single of the receivers is lifted, the circuit sends alternating present-day to the other cell phone, causing it to ring. When both equally receivers are lifted, the circuit sends immediate present-day rather, which makes it possible for the consumers to converse and listen.”
To get the first ringer to function, although, required at least 53V of ability — and with shipping to Burns’ office environment in Tbilisi, Georgia getting fairly as well long, the maker turned to a nearby out of doors market place and picked up a pair of classic transformers. The to start with, able of a alternatively abnormal 250A, places out 55V for the ringer the next places out 24V to travel the audio circuitry.
The parts list includes a vintage 55V 250A transformer, which proved functional if not a very little cumbersome. (📷: Thomas Burns)
With the transformers and manage boards housed in a reused steel housing, Burns was capable to wire up each phones — without having modification. “After a bit of troubleshooting encompassing the cell phone line connections, we last but not least got it all up and operating,” he explains. “The telephones ring as intended, and the receivers are transmitting and getting as we had hoped. The only factor I noticed was that the audio stage was a little bit small when listening and the audio is a bit crackly, but my pals who grew up in the USSR listened to it and informed me this was totally standard for Soviet telephones.”
Burns’ complete compose-up, which include a elements list and schematics for the handle circuit, is readily available on his project web page a video clip detailing the develop is available on the Workshop Nation YouTube channel.