Several replies received with good suggestions. Here is the summary.
SILICON SHEET
1. Use RTV Silicone Gasket material. This is available from most any
automotive supply shop.
I actually tried what I had on hand, Permatex ULTRA BLUE RTV Silicone Gasket
Maker 77B and the resulting bond between pieces is very strong. That is now
first of several gaskets for GS-35B amps. I would suggest 1/8 or 3/16 inch
thick silicon to obtain flexible yet rigid enough tube. My first chimney is
2.4 inches high
I did clean the surfaces several times with rubbing alcohol prior to
application of the RTV. Apply RTV very thin to both pieces then clamp
together firmlly. I used 2 small pieces of wood to get good clamp pressure
over entire bonding surface.
2. Use NYLON screws and nuts.
I did not try this solution.
TEFLON
1. Have chimneys machined from solid rod..
This would a very good chimney however VERY expensive.
2. Use tubing.
This would come in "standard" diameters and wall thickness and may be
difficult to find the correct size.
3. Make from sheet and secure with NYLON screws and nuts.
4. Make from sheet and use ordinary brown plastic (mylar?) parcel tape
gives good
results. W2GN made hundreds of these for the ARCOS VHF amps.
Use the tube anode as a former, and wrap the teflon sheet around it to
make about a half-inch overlap. Then tape crosswise over the joint with
a one-inch wide strip of parcel tape, wrapping it over the inside of the
chimney too. (I hope that's clear: the tape doesn't go around the tube,
it goes around the overlap in the teflon sheet.)
5. Contact a supplier that who makes TEFLON printed circuit boards and get
suggestions for bonding. This could result in some "nasty" chemicals
though.
Hope this info helpful to others.
73 de Arne N7KA
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