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A New Ultrasonic Heater

Posted by Triode_Kingdom on January 6, 2017 at 19:39:44:
I've been working on a revised circuit for this in my spare time. The design below is the result. It may look complex, but it's really only a small handful of parts, and it could be built on a very small circuit board. The output transformer can be wound to produce exactly the voltage needed for tubes like the 211 and GM-70. An additional, external transformer can be added for tubes that need 2.5V or 1.5V.
To explain the operation, this circuit is powered by +160V produced by a bridge rectifier/filter attached directly to the AC mains. When power is turned on, the startup circuit supplies about +5.5V to the comparator, sufficient to start the oscillations. A VCC winding on the transformer then produces a rectified voltage that takes over from the startup circuit and operates the comparator at full power, about +10V. Not shown, a 2A fuse between the +160V source and the primary of the output transformer protects the components from overload if oscillation ceases or the output is shorted. This circuit will oscillate at frequencies to at least 200kHz, depending on the RC values at the comparator.
This circuit was interesting to design, but to be honest, I don't have a lot of interest in building it myself. My SETs operate satisfactorily on the halogen units, and I don't plan to use ultrasonic heating on drivers or preamps. Any engineer interested in pursuing this should be able to take it from here. I modeled the circuit using a LT1713 differential comparator and IPB65R420CFD MOSFET, both included in the latest version of LTspice IV.