Has anyone ever tried this?

Muzzer, what you see is half of the class B (push-pull) modulator stage of a 250kW hf transmitter. If memory serves me right, in order to modulate a 250kW a.m. transmitter to 100% modulation you need 125kW of audio.

The 250 kW rf stage has two identical valves but in class C, also with vapor cooling.

By vapor cooling I mean water is boiled in the boiler the valve sits in and there is a small amount of waterflow to top it up which goes over a weir and flows down the pyrex tubes. The steam goes outside to be condensed and back in the tank. Hope I have this right from school but the latent heat of vaporisation of pure water is 539cal per gram, so by letting the water boil at 100 deg C, you can transfer the heat with 1/539 of the waterflow that would be required for water cooling at 99 deg C.

Incidentally, the valve sits on a viton O ring to seal it which is about 8in diameter and 1/4 in cross-section - just like a big version of what we might use on our locos.

When I drilled holes in macaroni at Stanmore we had a vibration test rig that ran 1MW across the audio frequency range. Nothing ever lasted 30 seconds the first round and they had to run an hour to pass. Housing estate now but some more of the products have just gone for a holiday in the Middle East.

Anthony, if you wish to modulate an Amplitude Modulation signal to 100%, you need similar audio power to RF power. The BBC only modulates to about 30%, I believe.

On a visit to Moorside Edge transmitting station near Huddersfield, in the days before the IRA was active, the engineer allowed a bit of the cooling water out of the PA anodes. As it was distilled water, ie a 'perfect' insulator, he could run it over his hand without receiving a shock from the HT supply.

Geoff

Still used, even in space applications.

Russell

That's one reason why FM radios (transmit side) are popular, you lose the need for a big audio amp to drive the modulation. Less power, less components, smaller cheaper radios.

I am indebted to you for this new information. The only thing I can add, politely, is both statements are incorrect.

Anyway, we are getting off-topic.