[R-390] Audio output transformer

[Graham Baxter]

Hi All

You may recall that I have been looking for an audio output transformer.

My friend John Branson offered me a cosmetically good transformer with
an open circuit primary. Of course I could not resist!

If there is any interest I will offer a web page for the rewind on the
lines of my filter repair.

In the meantime, so that it is recorded for posterity, here are the
turns counts.

The secondary has two windings, each of 417 turns. The entire
secondary when connected in series therefore has 834 turns.

The primary was not counted. The number of turns was calculated as
3152 after allowing for the effect of the resistance of the windings
on the impedance transformation ratio.

The measured diameter of the primary wire including the varnish was
0.0035 inches. I chose to use 0.071mm wire to allow for the varnish.
Had I had any, I would have used 0.08 or even 0.09mm since the
resistance per meter was higher than the original.

The diameter of the secondary wires was 0.0065" including the varnish.
I used 0.125mm .

It is now all reassembled, with minimal blemishing of the paintwork.
It is working very well although my primary resistance is a little
higher than it should be.

Graham
G8OAD