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Second try. The first posting disappeared.
For some time I had been playing with the idea of making a home brew Hegehog audio transformer.
The need became more urgent when I acquired a very early 20’s home brew radio of about 1922 vintage that had had two but they had been removed in the past. Wiring and witness marks indicated their prior installation.
As a guide I used the article “An Efficient Audio Frequency Transformer” from Radio News, July 1922.
A cardboard tube about 1 1/2 inches long with end caps was used as the core. The primary winding was 4000 turns of #40 wire and the secondary was 14,000 turns of #41. This was sealed with cloth tape and shellac
The core of the transformer was soft iron wire lengths, as many as would fit,, shellac coated and bent around the winding package. The transformer was inserted into a brass tube that had a copper mounting plate soldered to it.
The final turns ratio is 3:5 to 1. Primary resistance is 0.839K ohms and the secondary resistance is 4.70K ohms.
I have yet to try it in an actual radio if successful the second transformer will be made to complete the restoration.
Ed.
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