• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Powerdrive for higher grid wattage A2 transmitter tubes

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I've thought it would be worth trying direct coupling a tube driver stage to (a) CCS loaded MOSFET follower(s) and then use parafeed to a mains toroid with perhaps 25V secondaries for a medium power, low cost amp.

I recently did a bench experiment where I made a mosfet follower drive an Edcor gapped SE output transformer and drove the follower from a tube stage with a lot of swing. If I recall correctly, I got over 15W before distortion exceeded 1%. Mosfet followers can drive output transformers quite nicely.
 
Not all mains toroids will work as OPT's, but some do work quite well. Usually the larger ones come up a bit short on primary inductance, so feeding them with a low impedance source is the key to squeezing the most out of them.

Another trick is to find an isolation transformer with 4 120 volt windings and no epoxy in the center. Wire all 120 volt windings in series and wind a new secondary over the top of the Mylar overwrap. Try all the possible combinations of order in series connecting the 120 volt windings, especially if using it for a P-P OPT. The HF frequency response can be very different due to leakage inductance and winding capacitance.
 
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