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Re: Really Cheap Secondary Xfrmr Tube
I'd worry about residual moisture in the form if the polyurethane spray
is water based. Over the past 40 years or so I've made many quite
satisfactory forms for small coils, Tesla and otherwise, using the
following method:
1. If you work in an office, keep your eyes open for mailing tubes.
Otherwise look in trash bins. etc. I have found tubes up to 7" diameter
this way. (Whenever I see something suitable I immediately glomb on to
it.)
2. Cut to length and trim ends. Sand if surface is rough.
3. Bake in oven at around 250° for a couple of hours to help dry it
out. (IF your oven is big enough, that is.)
4. Apply a couple of coats of thinned shellac to the OUTSIDE and allow
to dry.
5. Peel some of the paper off the INSIDE of the tube. This is usually
quite easy to do, as it appears to be built up in layers. Experiment
with a piece for cutting form.
6. Coat the inside of the tube with thinned shellac. Can be done with
a brush with a long handle tied to it, or by capping one end, pouring in
shellac, holding the tube ALMOST horizontal (you don't want the stuff to
spill out) until coated, then pouring excess back in the container. I
prefer the brush method.
7. Dry in oven again.
8. Repeat the coating and baking of the inside and outside until the
form is really stiff and hard. When you are through you will have a
neat job which you will be pleased with.
This may sound hard, but it isn't really since it takes only a few
minutes per step, and you can do other things in between steps.
Ed
> I am using a cardboard tube for my secondary also,and I found that using
> spray type polyurethane works real well because it is so thin that if done
> right you can get the poly to soak all the way thru the cardboard.
> I am not sure if this helps to improve coil operation but it sure makes it
> moisture proof and real strong.
> One note,it takes a very long time to dry!!
>
> Safe Coiln'
> Kevin Dalpe