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Paper insulation for output transformers?

Paper have lower dielectric constant compared to mylar, polyester, kapton or woven fiberglass used for interlayer transformer insulation. Thus, you can achieve lower stray capacitance and higher resonant frequency.
Apart from organic press-paper (presspan), there is so called Nomex paper (flame resistant meta-aramid), which have both low dielectric constant and high resistance to heat and flame. For transformer insulation I would suggest adhesive tape, 12mm width, 0.1 mm thickness.

PS. Please change subject from "Paper output transformers" to something like "Paper insulation for output transformers", it would more clear on subject.
 
Nomex(410) is excellent but much much more expensive then paper or mylar(=polyester). Teflon has the same dielectric constant as paper but is also very expensive. Mylar is just cost efficient but not the right choice for audio transformers. Tribute for instance uses "paper" but that is pressed paper, very useable for audio transformers but normal paper is better because dielectric is lower. Nomex is also in many varieties so you have use a less pressed verion (410 or 411, other nomex types are less good then paper)


Yes, Nomex is 4x more expensive compared to mylar or polyester.
 
Traditional paper for transformers is called kraft paper which means brand new paper with no recycled paper.
I dont think recycled paper is really bad, just less strong

Papaer is a traditional transformer insulation. It is supposed to be a fairly high quality paper - high clay content perhaps? I have heard that some Chinese transformers use recycled newspaper - about the lowest quality paper made, very hygroscopic.
 
Any thoughts,
On the sound quality compared to other insulation materials?
Does it have an impact or can it be overcome with winding topology..

There is no direct impact on sound quality, but there is significant impact on other parameters of the transformer, which, in turn, may have considerable effect on sound quality and amplifier stability.

As I said before, organic paper and Nomex have lower dielectric constant compared to mylar, polyester, kapton or woven fiberglass used for interlayer transformer insulation. Thus, you can achieve lower stray capacitance and higher resonant frequency.

You can use fewer sections to reduce stray capacitance, but this will increase leakage inductance. You need to define your target parameters and constructional details of the transformer, and then decide if there is a need for more expensive insulation material.
 
Soft paper may allow windings to move slightly so allowing some transformer noise and possibly distortion. Hygroscopic paper will attract and retain moisture which could allow electrolysis to occur wherever the windings have a crack in the wire insulation - the result will be shorter lifetime before the transformer develops a shorted turn.

The right sort of paper will work just as well as any other insulator.
 
Paper will be always a little hygroscopic, the same is for nomex.
Both have been profed to be excellent over a long period of time without problems.
Maybe in a tropical climate there must be some precautions.
You can use wax to impregnate it.

Soft paper may allow windings to move slightly so allowing some transformer noise and possibly distortion. Hygroscopic paper will attract and retain moisture which could allow electrolysis to occur wherever the windings have a crack in the wire insulation - the result will be shorter lifetime before the transformer develops a shorted turn.

The right sort of paper will work just as well as any other insulator.