Those with an interest in the TV broadcast side of things...

[John Rumm]

May find this snoop around a now defunct analogue Tx interesting:

(warning, features strong aussie accents!)

[Graham.]

I'm actually surprised how small those 5kW valves are.

[nemo]

It's not actually much different to modern semiconductors. The limiting factor is how efficiently you can remove the heat by air or water.

[Andrew May]

Water cooled valves. Now there's an interesting idea. I bet someone has done it somewhere.

[John Rumm]

They don't scale that much in size from what I remember... I did some software development on some old Marconi transmission systems once. Their 10kW tuneable HF transmitter (H1141) had a similar sized valve[1] that could do 10kW out (and 16kW of heat up the chimney!))

The other side of the rig room in which I was integrating that, was a monster 2MW HF amp (the level setting audio preamp that fed it had a

250kW output just by itself). I was told the main valve in that was larger - but not dramatically so. (the coax on that made the one in the video look like a bit of limp string) [1] A two stage thermionic design again - semiconductor preamp stage, followed by penultimate and final stage valves. The first lifting to around 400W, and the big one at the end doing the bulk of the work.

[John Rumm]

Yup, seen it done on a commercial transmitter. Gets the size down quite a bit.

[Graham.]

1:53 in.

[Dave Liquorice]

IIRC the valves used for the 198 kHz Tx at Droitwhich are water cooled and they have some big goldfish in the pond...

[Mike Tomlinson]

In article , John Rumm writes

That was interesting, thanks for the link. Surprised at the sharp bends in the high-wattage RF copper tubes, would have thought that would be a no-no, analogous to kinking coax cable.

[harryagain]

Electric cars have watercooled motors and electronics. Radiator up front.

[Capitol]

Mercury arc rectifiers (ignitrons). Can handle 10KA surges, nearly indestructible up to around 300KVA per unit Very useful for 100A+ fuse testing.

[Mike Tomlinson]

In article , Capitol writes

wonder what the presenter did to his hand?

[Capitol]

Plastic!

[tony sayer]

In article , Mike Tomlinson scribeth thus

Pikey's delight here;)...

[Woody]

And remember, that is co-ax, not copper pipe!

[John Rumm]

In true Crocodile Dundee style, na, that's not a co-ax, *that*'s a co-ax (referring to the 12" diameter pipework that used to come out of the back of the 2MW HPA in the Marconi rig room... (it went to a huge cone shaped dummy load, that was water cooled, and the fairly substatial pipework for that fed a bank of fan assisted radiators in the car park (each abut half the size of a car)). IIRC they needed to phone the electric company to warn them when they were going to turn it on.