Electronics > Projects, Designs, and Technical Stuff
Strange AC current source..("variator"????)
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SuzyC:
Any MCU easily does the job.
dmills:
Build a bog standard constant current circuit (couple of diodes, bipolar transistor, emitter resistor, you know the drill), and wire it between the + and - terminals of a bridge rectifier, connect the AC terminals to the rest of the circuit.

Regards, Dan.
mikerj:
Should a tube heater be driven with a constant current?  I'd have thought the tungsten filament would have a positive TC, making constant drive undesirable.
ArthurDent:
mikerj - "Should a tube heater be driven with a constant current?  I'd have thought the tungsten filament would have a positive TC, making constant drive undesirable. "

If you check the reference in my post above, you will see how these constant current ballast tubes do a pretty good job to control a tube heater voltage. These ballast tubes were designed around the 1930s long before solid state voltage regulators were available to do a much better job.   
David Hess:
Precision vacuum tube circuits regulate the heater voltage or current to prevent offset voltage changes.
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