|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: mylar insulation vs polypropylene vs paper vs nomex vs teflon posted by Bas Horneman on March 18, 2003 at 01:17:20:
Hi Bas:you ask which I like best of the candidates listed above.
Tough to give a hands-down... this "guy" is the winner because in addition to electrical characteristics and sound quality you must also consider physical properties and characteristics of each of the materials.
for signal handling I can say that I don't care for the sound of mylar at all. It's physicals are pretty decent and it's electricals in terms of voltage breakdown is pretty good and it's decently non-hygroscopic... another quality or characteristic of mylar is that it does not absorb the impregnant... which can be "good" or "bad" again depending on circumstances and what impregnant your using.
polypropylene sounds good to my ears but it's most serious drawback is that it melts (or becomes decidedly plastic
) around 185 degrees F. If your heating up your units to drive out the moisture before you impregnate or you've used adhesive tapes with a thermoset... your going to have to bake your trans well above 185 degrees for a few hours... and the polypropylene just won't be happy with this at all. that leaves paper, nomex, and teflon.
First the teflon. Love this stuff. And, no, I have never been able to hear it ring or cry like a little bell such as one esteemed audio guru claimed in print many years ago. But, actually, you have to break this down and ask what type of teflon? Are you talking PTFE or FEP? Both have near identical electrical characteristics but widely different physically. The FEP is much stiffer and does not cold flow nearly as much or as easily as the PTFE.
Actaully, the "bell" story I mention is really halirious when you stop and consider that PTFE is so mushy a material that how you would get this lossy material to naturally ring is one of the great unsolved mysteries of all time to me. Rather, it characteristic "softness" is a bit of a restraint on it's use... it has no "platform strength" so essentially cannot be used in say hand wound coils using what is called "perfect layer winding".
the FEP can be used in a perfect layer winding... it is much stiffer than the PTFE.... but it like PTFE remains slippery... which presents another problem with layer winding with either type... keeping the winding down exactly where ya wound it....
in bobbin winding (sometimes called random winding... which good jobs are not (random that is)) the slipperiness is less of a problems since you have end cheeks which will keep the windings from falling out of place... and assuming your using essentially a *100percent*
fill across the "B" dimension of the coil.teflon has good voltage breakdown strength but very, very poor corona resistance so you might not want to use it on your 211 output operating at 1250 vdc and then carrying a few hundred volts of ac signal on top of it...
teflon does not absorb impregnants very well but withstands baking temperatures really well. I use a lot of teflon in our bobbin wound products.
Paper. Nice stuff. Sound is not most transparent but does give (especially if wax impregnated) a nice, rich harmonic tone structure and good body. A little bit more "old timey" sounding... but smooth.
Best way to wreck paper insulation is to use nasty varnishes. Thepaper wicks (depending a bit on how much it has been calendared) the impregnant and absorbs it into it's self... use wax and you get a really nice "sorbathane" effect... varnish on the other hand dries out the paper and makes it brittle.... which is why on an old trans that you take the bells off of you can apply finger pressure and the paper will crack under just this bit of pressure. wax it instead of varnish and this problem is alleviated almost fully. Paper loves wax impregnation.But... don't use paper inside a bobbin. Paper is hygroscopic. It will absorb moisture and it's dielectrics are altered (unfavorably) plus it's voltage breakdown properties are adversely effected. Ensconced in a bobbin there is essentially no way to impregnate the paper... and hence it will be "dry" or "unimpregnated" for the most part. Just not a good idea or good choice for bobbins. In layer wound coils paper can work well and sound good like I have described above.
Nomex. Great stuff. About twenty times more expensive than paper... several times more expensive than even the PTFE teflon. great mechanicals. great dielectrics. strong and stiff. but bear in mind that there are several different types of nomex available and that their electrical properties (and physical) vary with the grade and thickness of the material. Dielectric constant with the right grade and thickness is lower than the constant of teflon.
Beautiful stuff. I use it in a lot of my hand wound "perfect layer" coils. Sound? Very neutral with a lot of transparency and no hangover effects... not a "lasy" sounding dielectric. Use wax to keep the good sonics... not varnish.
So... Bas... I hope I've shed some light on insulating materials and the use of them in audio transformers. sorry if I couldn't give you a strict ordinal ranking.And the last thing I want to do is to "buzzword" insulations... or make folks think that insulation is the only key to a good design. As I have always said.... a good tranney (like any other complex product) is getting 437 things well or good or at least holding hands together in a harmonius way.
But... that folks worry about a ten percent difference in nominal advertised impedance and nary give any thought at all to the quality of materials inside the transformer.... well, that little microscope (tunnel vision) might actually harm their ears.
cheers,
MSL
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: mylar insulation vs polypropylene vs paper vs nomex vs teflon - MQracing 20:23:12 03/18/03 (1)
- Thanks Mike! Good post. - Bas Horneman 02:37:16 03/20/03 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
