The size of this transformer is about 5.5cm x 5.5cm x 4 cm.
It seems to be a E E Philips ferrite core. The 2 Es are assembled facing each other. 2 pieces of paper were placed between the outer edges of Es for making 2 air gaps ie for avoiding core saturation from DC current flowing through the transistor operating in class A. Class A means electrons are flowing all the time.
A long piece of thinish wire was used to wind 4 windings in series without interruption.
Similarly another 4 windings with a thicker wire for the speaker output.
So various combinations of primary or secondary impedance are allowed.
The primary winding is made of 4x 140 turns.
The secondary winding is made of 4x35 turns.
Inductance at various taps of primary winding before inserting Es is
15mH, 2mH, 3mH, 4.6mH
After inserting Es and one paper spacing (on one edge of Es) inductance transformation is
600mH : 40mH
After inserting 2 papers on both edges of Es, inductance transformation is:
340mH:20mH
and this is currently used for listening tests with a Pleiades BD139 one transistor power amplifier.
See next post.
Later addition: when connecting the 4Ω Tesla fullrange speaker (linoleum Pleiades Auratone 5C type small cube) at the loudest sounding terminals, the measured impedance reflected to the primary winding is 180Ω.
Later addition: the transformer cores may be Philips?, or Ferroxcube? ETD 48. The core may be 3C90. Smaller size ETD 39 or ETD 34 has not yet been tried.
Datasheet: https://elnamagnetics.com/wp-content/uploads/library/Ferroxcube-Materials/3C90_Material_Specification.pdf
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