Winding an output transformer for PL36 push pull

[Boater Sam]

I'm putting together an amplifier using all TV valves.

Push pull output with PL36s, got loads of them.

The question is, do the primary windings of the transformer get wound on the bobbin/s in the same direction relative to the core or are they wound opposite ways, if so why?

I have never wound a push pull transformer hence the query.

To reduce the capacitance this will be wound on 2 bobbins, half the primary and half the secondary on each bobbin with the windings cross connected in series. I assume I connect end of one to start of the other?

Been reading books on how to do it but can't find answers to these questions. This is the trouble it gets you in to.

[Peter.N.]

It will in effect be a continuous winding tapped in the centre, so both halves will be in phase from end to end but in opposite phases when fed from the centre.

Peter

[Diabolical Artificer]

Have you read this Sam - http://www.dissident-audio.com/Trans...ign_Manual.pdf ? More stuff here - http://www.turneraudio.com.au/output-trans-winding.htm and here - http://www.turneraudio.com.au/output-trans-winding.htm and here - https://ludens.cl/Electron/trafos/trafos.html and lastly some ifo regarding your question here - http://deerloverssite.org/TRANSFORMERS.html

Andy.

[Boater Sam]

Thanks Andy.
I had found some of these sites but more is always better,
Plenty to read, won't need a paper today!
Sam.

[Al (astral highway)]

Originally Posted by Boater Sam

To reduce the capacitance this will be wound on 2 bobbins, half the primary and half the secondary on each bobbin with the windings cross connected in series. I assume I connect end of one to start of the other?

Hey Sam, Ed (Dinning) is the transformer winding expert here, but I would have thought that the self-capacitance of an iron-cored transformer for audio frequencies is so negligible compared to its inductance as to be ignored?

[Ed_Dinning]

Hi Al, the problem with the self capacitance becomes apparent when there is feedback applied to the amplifier, usually resulting in instability.

Ed

[kalee20]

Originally Posted by astral highway

...I would have thought that the self-capacitance of an iron-cored transformer for audio frequencies is so negligible compared to its inductance as to be ignored?

Unfortunately not! If you have enough turns to get decent low-frequency performance, you tend to have enough to give a few hundred pF of stray capacitance, which can start to hurt at not much more than top-end AF. Even if it doesn't start to give serious roll-off within the audible range, it can give enough phase shift, with other strays, that the amplifier goes unstable, just as Ed says. And the cure for that might be to introduce a dominant roll-off which just HAS to be in the audible range.

Iron-cored transformers, as used for inter-stage coupling, are quite difficult to make if you want a frequency range of more than 10 octaves (say 20Hz - 20kHz). Even 8 octaves (40Hz - 10kHz) is a challenge!

[Boater Sam]

Its wound and working.
2 bobbins side by side, 1788 turns primary on each, 29 turn secondary on each. 1 inch square core laminations.
Primary resistance came out at 568 Ohms overall.
Ran it up on a pair of EL33s, 288 volts on the anodes, sounds fine. Very loud!
I'm encouraged to try bigger!