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Old 14th Oct 2019, 1:10 pm   #20
Mr 1936
Heptode
 
Join Date: Mar 2017
Location: Romsey, Hampshire, UK.
Posts: 511
Default Re: Osram Music Magnet 4

I was faced with an open circuit intervalve transformer in a 1929 suitcase set.

With no facilities for home rewinds, I instead successfully used a miniature commercial microphone transformer from OEP (Oxford Electronic Products). It was possible to fit this within the original transformer case.

The OEP unit has centre tapped nominally 600 ohm primary and a 3.75 K secondary. Using the whole of the primary results in a turns ratio of 2.5 to 1

For those who might be interested, the size is 36 x 30 x 25 mm, the part number J30A11C and it's stocked by RS as 123-7215. Not cheap at £52, but an instant solution and depending on how you price your own time it might be an option. See the RS website for a data sheet.
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