[Amps] Chimneys for Russian tubes

[Ian White, G3SEK]

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