New Mosfet PA for remote operations

Last week on 50MHz I’ve lost the QSO with KH7Y due the low power when controlling my station from the workplace. I don’t want to leave the tube PA switched ON when not at home…

So I’ve built a compact solid state 6m amplifier using hardware found in the drawer

It doesn’t look good but works fine.

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Mosfet are a couple of SD2933 mounted on a large heatsink, supply is 2x 50V 10A switching (about 30eu each on ebay) and an old laptop supply for biasing/services, output relay is a Magnecraft.

The design is a classic push-pull with input matching in a single step and output matching in 2 steps to keep “Q” at reasonable level.

I had to use a full 1/4 wavelenght balun as a phase splitter for a perfect balancement. I’ve tried also a lambda/16 balun with worst results.

Everything was projected with the aid of Linsmith and simulated with Qucs

Power output is somewhat greater than 500W with 11W input.

The output spectrum is good even without the use of a filter,  thanks to the push-pull configuration that kills the 2nd (and the other even) harmonic.







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