Hello all
I've been off this reflector for a few weeks - hope my
comments are relevant to this cooling discussion.
I have a homebrew amp. with a single QY5-500
(looks a bit like a large 3-500z) which is cooled by
a side-mounted fan - there is a definite difference
in temp. between the side of the valve nearest to the
fan and the side furthest away. If I was rebuilding this
amp. I would use a fan blowing up from below + a
glass chimney, or some better method.
However, I was under the impression that most of
the heat given off by e.g. 3-500Z-type valves is in
the form of infra-red radiation from the anode structure,
a proportion of which will be absorbed by the glass/
quartz envelope and raises the temperature of this
envelope. Some valves seem better at allowing this
infra-red to pass through and heat the surrounding
metalwork etc, than others.
In the Ameritron AL-80 (single 3-500ZG) I have, the metal
case gets very warm after a relatively short time of use,
and takes about 10-15 minutes of cooling without
transmitting to return to room temperature. I suspect
that the 3-500ZG has cooled down much quicker than
the metalwork.
What's the point I'm trying to make? - just that it seems
to be the valve seals that are the crucial area for
cooling, and that blasting air at the glass envelope
isn't really achieving much - yes the glass envelope
needs some cooling, but why are the insides of the
P.A. compartment in these amps. not painted matt
black ?
73
Chris GM3WOJ
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