Because it is hard to imagine enough output tubes to handle even 2 amps of idle current, a hybrid Circlotron amplifier is shown. The output stage runs in pure, real Class A and it will get hot even with its small solid-state rail voltages. The first tube provides all the voltage gain; the second tube, the phase splitting; the MOSFETS, the current gain; the Op-Amps, the DC servo housekeeping. Should one fuse blow, the opposing Op-Amplifier's positive power supply connection is lost and its output voltage must collapse to zero volts, which turns off the opposing MOSFET.

   We have a starting point to making safer tube equipment. Begin by having a good amount of respect for the high voltage's lethal nature. Then ask yourself, What happens with a cold tube? What is a safe rating for a part? What happens when a component only partially fails?
What happens when the fuse blows?


Hybrid OTL amplifier with safe fuse arrangement


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