Popular Electronics Magazine April 1955

Posted on Feb 6, 2014

When I spotted this April, 1955 issue of Popular Electronics magazine at a swap meet, I practically left burning rubber on the floor as I rushed over to grab it. Theremins have always interested me, and I had been seeking this issue for a long time after spotting one (ovepriced!) in an online auction. The cover depicts a dreamy-looking gent playin

Popular Electronics Magazine April 1955
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g his homebuilt Theremin. Theremins were among the very earliest electronic musical instruments. Invented in the 1920s by a Russian, Leon Theremin, this namesake instrument is played without any physical contact between the musician and the device! You merely move your hands in the air near two antennas to control the Theremin`s pitch and volume. The magazine contains plans for building this Theremin. Using five tubes (5Y3GT, 6AU6, 6AT6, 6BE6, 6C4), the device uses a transformer-type power supply and and is constructed using a standard 1950s amplifier chassis and housing. Most Theremin antennas take the shape of simple loops or poles. In this design, the antennas are terminated with large sheet-metal letters, T for tone and V for volume. Below is the schematic and basic technical description. In operation, the signals from a variable frequency RF oscillator (the 6C4 stage) are combined with the signals from a fixed frequency RF oscillator in the mixer stage (6BE6). The difference frequency output, an audio frequency, is fed through a filter circuit to remove any RF signals that might remain and then to a variable gain amplifier (6AU6). The amount of amplification given by the 6AU6 stage depends on its grid bias and this, in turn, depends on the output of a third high frequency oscillator (6AT6). One antenna permits the operator to vary the frequency of the 6C4 oscillator ("T" or tone control antenna) and hence the pitch of...

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