Hi Patrick,

I think Yves talked about transmitting tubes
in satellites. No air stream or water flow to
cool them in space ... only radiation cooling
is available out there.

Surly there are internal cooling systems like
heat pipes leading the heat power from the point
the heat origins from (e.g power tube plates,
or the nuclear reactor "batteries" often found
in military satellites) to the radiation cooling
fins at the outside of the satellite, but in the
end it is all pure radiation cooling to get the
heat power away from the satellite structure/body.

And with water cooling, the tubes could be small,
and no trouble for 500 watts of dissipation.

As far as I know, HAMs sometimes put generic RF output
stage tubes "upside down" into oil baths and run them
_way_ beyond their nominal "air cooled" dissipation.
Together with intermittend CW morse/pulse operation
they draw power ratings from a 6L6 (or what else they
use) which would make us AF types simply _faint_.

Probably HAMs lurking here due to the AM radio thread
can elaborate a bit ...

Tom "hurrying to order a 1cbm tank full of SF6 at
-20C to drown my ECL82PSET in which surely will
be good for 1,5 KW sustained AF power then ;-)"

P.S.: Don't try liquid nitrogen, the temperature gradient
in operation would be too steep for the glas envelope ...

--
A gleekzorp without a tornpee is like
a quap without a fertsneet (sort of).