Jay:

In theory, there is no reason the silicon chimney won't work, as most of the surface area is actually in the fins inside
the circumference, and not the outside diameter at all. The minimal additional area you get by having a looser fit
chimney is likely marginal.

However, at a hundred bucks, I can certainly see a dozen other ways to get a chimney in place for a LOT less money, and
nearly as neatly as well. Hell, even an aluminum sleeve closed with a couple of pop rivets, though far from
aesthetically optimum, will keep the tube nice and cool (given the same blower capacity) and for only a couple of bucks,
tops... There are times to spend outrageous sums of money and this isn't necessarily one of them (at least for my
budget, anyway).

Of course, if I were actually building a 5 kW capable linear, I probably would have far more money than sense,
particularly if you expect it would be used on the CB Band, and even on the Ham Bands (at least in the US) it is so far
into illegal territory that you'd probably not give a damn in the first place. Therefore, the cost of the silicon
chimney is probably a mere pittance, compared to eventual costs of defending the eventual litigation from running such a
linear... [sigh]

Oh, wouldn't it be nice to have so much disposable cash as to not really care the consequences....

--Rick



Jay in the Mojave wrote:

Hello All:

Look at this e-bay auction for high temp Chimney's. Pictured is a
3CX5000 Tube. Yeah I know only a driver, hehehehe

But I thought that the Chemney needed to have a .050 inch clearance
between the ID (inside diameter of the Chemney) and the OD (outside
diameter of the tubes plate. Allowing air to flow over the outside of
the tubes plate OD surface. Or is it ok to use such "Silicon Rubber
Chemneys" forcing all the cooling air thru the tubes inner plate cooling
fins?????

http://cgi.ebay.com/4CX5000-YC156-Si...cmd ZViewItem

I have seen these Chemneys on production model amplifiers.

Jay in the Mojave