Coil Dope Subsitute
 

After winding a RF coil, I like to dope it to keep the winding tight. I finally ran out of the dope I bought many years ago and looked around to replace it. The only kind that seems to be readily available now is the polystyrene type which I found to be a poor substitute as it does not grip either the wire or the former very well.
I had some gloss polyurathane varnish left over from a hardwood floor refinishing project so thought I would try an experiment. I wound a coil and measured it on my Q-meter as 200 at 20 Mhz. Then I used the floor varnish on it and remeasured the Q after the varnish dried. Still 200, and the varnish gripped the wire and the coil former just like my old coil dope did.
So polyurathane varnish makes a satisfactory coil dope.
John.

Re: Coil Dope Subsitute
 

Polyurethane is used for insulating tesla coils that operate at many KV. RS Components also sell an insulating spray varnish that would also do the trick. If your going to use off the shelf polyurethane varnish I would advice that a clear one is chosen, since the affect of any filler or pigment may have undesirable affects. Very small pots of clear polyurethane can be bought from model shops.

Regards Chris

Re: Coil Dope Subsitute
 

I would suggest that anyone using polyurethane varnish uses the gloss variety. It is much harder than the flat type which contains a high proportion of fillers.

Cheers