[turretslug]

My maternal grandmother used one of these devices, a "6m diathermy set" as a private physiotherapist. It used 2x 3C150A triodes in a self-rectifying push-pull circuit with a coarse power output switch selecting 1.5- 2.5kV tappings on the large mains transformer and a thermocouple meter giving an idea of the power level. Mains voltage adjustment was by what were effectively large L and N in-line banana sockets applied to primary 150 - 250V tapping panel plugs on the rear panel- the 150V tapping certainly stuck in my mind as signifying "another era". ISTR sometime in the early '80s, she downsized house and the diathermy set was amongst many things that had been skipped by time I registered an interest- something I regretted, though that might have helped me stay to alive as a tinkering youth.... Inside, it was a sight to behold- despite the high voltages, it was all in neat parallel and right-angled un-insulated thick single copper wire linking valve-holders, switches, hefty tuning coils all constructed or supported on chunky ceramic bases, I recall that even the common grid resistor was like a chunk of finely-wound bar-fire element!