Used to maintain diathermy equipment back in the dark ages.
My favorites were the Siemens brand made in Germany. Had a 250-Watt glass triode with a graphite anode. Used a power oscillator circuit, with just the one tube, no separate oscillator or driver stage.
A servo motor turned the plate tune capacitor in and out of resonance, pulsing the RF up and down. Had to shut down any computers in the room before firing them up. If the two applicators were out of balance, it would radiate enough RF to crash them.
Can't say I miss that stuff.
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