On 26/01/2021 09:52, Chris Green wrote:
Chris Holmes wrote:

One for Brian???

I was wondering back when men were men and Libby Purves worked on the other
side of the mic, radio transmitters used valves.

Are there now solid state devices (big MOSFETs??) capable of producing the
necessary output power? Or are valves still used?

There are big semiconductor devices capable.

However old transmitters are expensive to convert to new devices. I
seem to remember that the Radio 4 transmitter on 198kHz is still a
valve and that they only have one more spare.

The only one spare is ********. When the spare is placed into use, the
one removed goes back to the manufacturer to be rebuilt.