Amp Circlotron

Posted on Feb 7, 2014

It`s a power amplifier configuration that was developed in the 1950s. It is called a circlotron because the original idea diagram was drawn as a circle. The best I can do with my graphics program is to show it as a bridge. It`s promise is very low distortion. It`s cost is a total of 3 power supplies, none of them connected in common. Some amplifiers were commercially produced using this circuit.

Amp Circlotron
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They were high end units because of the high cost to produce. The circuit never caught on because the design had shortcomings which caused it to be unreliable. Here is the simplified schematic of a circlotron power output stage. B1 and B2 aren`t really batteries but represent totally floating power supplies. The battery marked C is the bias supply. Because each power supply has its negative terminal connected to one side of the output transformer, each channel of a stereo amplifier requires its own pair of power supplies. Commercial stereo amplifiers would have been made with a power transformer having 5 B+ windings. Two for each channel and the fifth for the preamp, drivers, and bias supply. Note: The bias supply is usually stolen from the B+ winding, or a tap on it, so a separate bias winding was not necessary. The positive of the bias battery is grounded so a single supply could have been used for both channels. Each tube is working as a cathode follower so its gain is a little less than unity. For a 50 watt amplifier the driving voltage is more than your airconditioner needs to run. It is not easy to develop this much audio voltage, even at low power, without introducing a lot of distortion. Some readers have objected to the use of the term "cathode follower" to characterize the tube configuration in this circuit. They argue that the plate is supplied a signal which is out of phase with the grid and cathode voltage...

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