Paul Whatton wrote:
Hi all, I'd appreciate some advice.
I'm building an amp with a pair of GI-7bs and will be blowing into the
anode compartment and using two PTFE chimneys in the usual (K2RIW) way
venting out of the top of the case. But because the Russian tubes have
open sided anode fins I wondered if it would be better to take the PTFE
chimney right down to the bottom of the cooler, thus creating a tunnel,
or only part way down the fins to allow some air flow through the sides
as well? The latter would certainly appear to help where the underside
slots in the fins are obstructed by the tank circuit bracket, but how
about all round?
Take the chimney most of the way down, so that most of the air has to
flow past the joint between the bottom of the cooler and the top of the
anode, which is the real hot-spot.
Some of those so-called "flat" surfaces are pretty bad - you wouldn't
tolerate that kind of roughness on a heatsink or the bottom of a power
transistor - so it might even be worth skimming them on a lathe.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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