[Amps] Chimney Construction

[Ian White, G3SEK]

ARNE  GJERNING wrote:
>Looking for best method to bond silicon rubber sheet 1/8 and 3/16 thick for
>tube chimney.  About 4 inch id.  Have heard this is not easy task.
>
>For TEFLON sheet 0.030 thick what is best method for same 4 inch id.  Was
>given sample piece 15x36 inch x 0.030 thick, price was right.  I know TEFLON
>is difficult to bond.
>
>Chimney lengths will vary from about 2 to 6 inches in length.

With teflon, 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.)

This method is less good for sheet as thick as 1/8 or 3/16in... so don't 
use thicker sheet already - there's no need for it.

On the other hand, if you already have the thick silicone rubber, try 
sticking it with clear silicone sealant. If the rubber seems greasy, try 
"priming" the overlapping surfaces first with a strong degreasing 
solvent. Wrap tightly over the whole chimney with PVC tape, to hold the 
entire length of the joint firmly together until the adhesive has 
thoroughly set.



-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                            Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek