I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

Kind regards, Eike
--

"Eike Lantzsch, ZP6CGE" wrote

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

I think it creeps but I'm not sure. I wonder if gasket paper is a
good dielectric? Dunno if it can be found anymore either.

cheers, Ian

"Eike Lantzsch, ZP6CGE" wrote:

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

Engineer's supply stores should sell copper shim material;
search around and there should be somebody from whom
you can purchase thin copper sheet which can be soldered.

I would never plumbers tape for transformers.
It's meant to squash up easily as a tapered thread is tightened,
and that's all.

For trannies where neat layered windings are used, flat strips
of neat fitting polyester sheet or maybe nomex should be used,
or the special electrical paper or cardboard for mains trannies only.
For random wound windings as used in small transformers,
polyester tape can be wound tightly, which will follow the uneven
contour
of the randomly wound coil.
Such transformers as used for 5 watt amps need only a start layer of
secondary, then say 3,000 randomly wound turns, then a finish secondary,

and the item usually will have enough bandwidth for a triode,
and the use of about 4 layers of 0.1 mm thick rugged polyester tape
will do fine without creating too many local pressure spots.

Toroidals use wound on polyester tape about 1" wide between windings,
with generous overlap, and so that any point there may be about 3
thicknesses
of tape between the windings, pulled tightly over what are usually
very unflat surfaces created by the gaps between the wires around the
outside
of the toroid.

Patrick Turner.



Kind regards, Eike
--

Ian Iveson wrote:
"Eike Lantzsch, ZP6CGE" wrote

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

I think it creeps but I'm not sure. I wonder if gasket paper is a
good dielectric? Dunno if it can be found anymore either.

cheers, Ian


Ian:

I guess that P.T. is right with the problem of teflon tape. And then
you are right as well that it creeps .
Polyester tape is what I was looking for but did not find. I'm in a
3rd world country. BUT gasket paper is still available here in a
variety of thicknesses. I will try that. Thanks.

Kind regards, Eike
--
Why postpone until tomorrow what you can avoid alltogether?

"Eike Lantzsch, ZP6CGE" wrote:

Ian Iveson wrote:
"Eike Lantzsch, ZP6CGE" wrote

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

I think it creeps but I'm not sure. I wonder if gasket paper is a
good dielectric? Dunno if it can be found anymore either.

cheers, Ian


Ian:

I guess that P.T. is right with the problem of teflon tape. And then
you are right as well that it creeps .
Polyester tape is what I was looking for but did not find. I'm in a
3rd world country. BUT gasket paper is still available here in a
variety of thicknesses. I will try that. Thanks.

Polyester sheet is maybe more common than you realize.
Its used in oven bags for cooking, and available at some supermarkets,
although maybe you don't have supermarkets with a wide variety of
goods where you are.

For OPTs, if you have no polyester to use then gasket paper
may have to suffice, despite the higher dielectic losses that
effectively raise stray capacitances and reduce the HF bandwidth.
Just make sure it isn't the slightest bit conductive, and that
the thickness suits your needs, so measuring 10 thicknessesses piled up
and dividing the total measured by 10 will give you the paper's thickness.

For vanishing, electrical grade varnish is the best because it can
withstand a
vacuum without vapourizing in a vacuum chamber during impregnation.
But if you have none of that then perhaps you have to settle
for soaking a pre-heated tranny
in some slightly thinned polyurethane furniture varnish.

But one should allow a long soak at various angles in a vat,
or liberally paint each layer of wire and paper insulation as it is wound
on,
and then you *know* the paper is soaked with varnish.
When the bobbin has the E&I inserted, and the bolts and yokes are
tightened
and the bobbin wedged tight with scraps of kitchen bench top
finishin material, then you still need to soake the whole thing
in varnish to impregnate any loose voids in the core.
Such benchtop plastic is about 1mm thick, and available in small pieces
as scrap from a joiner, if you can find one.
Some hardwood timber carefully planed down to 1 mm
is also good for shimming in a transformer when there is nothing else
around.

Polyurethane soaked trannies should be drained after soaking and then bake

for 4 hours in an oven at 130C, so a reliable little oven is needed.
The temp at the bottom of such an oven is less than at the top,
so like a roast dinner, you have to turn the tranny upside down after the
first 2 hrs. Surface varnish should be slightly browned, since it is
being oxidised, but inside thre tranny, the varnish should have cured
so that nearly all the solvent is expelled, and the varnish
has turned to a kind of adhesive, with just a bit of give, but sticky.

The varnish impregnated into the paper or cardboard
will make a kind of board when baked, and considerably increase
its life and ruggedness.

Waxing is also the other option, but really only good for
OPTs which usually have very low T rise.
You cannot paint molten wax on as you wind because it
will build up into layers too thick as it cools.
So the itm must be fully wound dry, then soak waxed
when done.
Candle wax alone is the minimum, and easily available,
but maybe you can get some furniture wax that is harder when
solid and which has a higher melting point.
The wax needs to be at about 100C, no more, so its viscosity
is like water, and caplilliary action draws it into the wind up,
and expels the air easily depending on how you orientate the item in the
vat,
and how well you have drilled plenty of holes in the bobbin cheeks to
allow
air and wax to flow in and out of the bobbin.
If you have no bobbin cheeks, then the tranny can be lowered into the vat
of
varnish or molten wax with the axis of the coils verical, to allow air to
easily bubble out
while the liquid spirals into the spaces between wires from the bottom.
When no more bubbles appear, it is soked well.

Patrick Turner.












Kind regards, Eike
--
Why postpone until tomorrow what you can avoid alltogether?

Patrick Turner wrote:


"Eike Lantzsch, ZP6CGE" wrote:

Ian Iveson wrote:
"Eike Lantzsch, ZP6CGE" wrote

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

I think it creeps but I'm not sure. I wonder if gasket paper is a
good dielectric? Dunno if it can be found anymore either.

cheers, Ian


Ian:

I guess that P.T. is right with the problem of teflon tape. And then
you are right as well that it creeps .
Polyester tape is what I was looking for but did not find. I'm in a
3rd world country. BUT gasket paper is still available here in a
variety of thicknesses. I will try that. Thanks.

Polyester sheet is maybe more common than you realize.
Its used in oven bags for cooking, and available at some supermarkets

[snip and more snippage below]

This did never occur to me. I will have a look around.

For vanishing, electrical grade varnish is the best because it can
withstand a
vacuum without vapourizing in a vacuum chamber during impregnation.

Electrical grade varnish is available locally. I am not too fond
of wax for LF-transformers - use it just for HF-transformers if they
do not get hot. Carnauba wax is available locally - but no - too
tedious for OPTs.

Thank you Patrick for your detailed instructions for impregnating.
I will now go and shop in some little thought-of places. Maybe I
can eventually make some fairly good SE OPTs for my pair of 8417s.

Kind regards, Eike
--
Competition: There will always be somebody who can make the same
thing cheaper and inferior.

"Eike Lantzsch, ZP6CGE" wrote:

Patrick Turner wrote:


"Eike Lantzsch, ZP6CGE" wrote:

Ian Iveson wrote:
"Eike Lantzsch, ZP6CGE" wrote

I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

I think it creeps but I'm not sure. I wonder if gasket paper is a
good dielectric? Dunno if it can be found anymore either.

cheers, Ian


Ian:

I guess that P.T. is right with the problem of teflon tape. And then
you are right as well that it creeps .
Polyester tape is what I was looking for but did not find. I'm in a
3rd world country. BUT gasket paper is still available here in a
variety of thicknesses. I will try that. Thanks.

Polyester sheet is maybe more common than you realize.
Its used in oven bags for cooking, and available at some supermarkets

[snip and more snippage below]

This did never occur to me. I will have a look around.

There is also polypropylene, a relative to polyethylene,
but both are low temp materials, not good for mains trannies.



For vanishing, electrical grade varnish is the best because it can
withstand a
vacuum without vapourizing in a vacuum chamber during impregnation.

Electrical grade varnish is available locally. I am not too fond
of wax for LF-transformers - use it just for HF-transformers if they
do not get hot. Carnauba wax is available locally - but no - too
tedious for OPTs.

Thank you Patrick for your detailed instructions for impregnating.
I will now go and shop in some little thought-of places. Maybe I
can eventually make some fairly good SE OPTs for my pair of 8417s.

Good luck



Kind regards, Eike
--
Competition: There will always be somebody who can make the same
thing cheaper and inferior.

And always someone who can make something better and more expensive.

And a pile of wannabes who make it cheaper, but who claim its better.....

Patrick Turner.

Can a person use mylar packing tape to secure layers? 10 mil and 15 mil
nomex sheets are available at your local motor rewind shop. Not cheap but do
the trick. There is also an air dry varnish made for electric motors. An old
pressure cooker, vacuum gage and vacuum pump works well together.
Regards,
Gary...
..
..
"Eike Lantzsch, ZP6CGE" wrote in message
...
I have a problem finding proper isolation foil for transformers.
What has to be said about the use of plumber's teflon tape between
windings?

Kind regards, Eike
--