Rewinding an induction coil

[countryman]

After I found the correct handset for my German ZB SA 24 phone, I noticed that the receiver volume still was low, no matter the handset tested good before. After checking anything else I measured the resistance of the sidetone induction coil, it should be 29 and 32 Ohm. It was 31 an 15, obviously some windings were shorted out.
After replacing it with a more modern IC (leaving the anti-sidetone winding unused) the phone worked good. I examined the old IC and found it could be disassembled fairly easy - the core laminations could be threaded out one by one.
Luckily the defective winding was the outer one. To my surprise it was patched together from 3 pieces of different wire! Obviously the factory used up what was available in 1925. It is very well possible that the phone left the factory in this condition and never made it's users really happy for this reason! Maybe it was even set to the side and survived thanks to it's frowsy assembly...

I decided to re-use the same wire and give it a try, possibly  the defective isolation would not interfere again . In fact I now measure the exact resistance values. I have not mounted the IC again but I'm pretty much convinced it will work now.

Because I know that quality tools are important, I used a winding tool of a renowed Danish brand ;-)

[RB]

oh, that is tooo funny lol

[Jim Stettler]

Because I know that quality tools are important, I used a winding tool of a renowed Danish brand ;-)

I used to have a field produced winder for watchcase receivers . It was made from the front of a woodie and a magneto. The effect was basically the same.
Good job,
Jim