[David G4EBT]

On with the field coil re-wind.

First I checked the gauge of the wire and weight it to see roughly how much I'd need to buy.
The resistance of the coil needed to be 2,000 Ohms and the gauge was 38SWG - 0.52mm. I calculated from the ohms per meter for that gauge that 2.3 KMs of wire would be needed, and that a 500g spool would be more than enough. I used the original coil tube, but not the cardboard end cheeks, as they were too flimsy, so I used them as a pattern to make new Paxolin cheeks which I fitted to the tube with two-part epoxy. I used solderable wire from wires&co.

The second pic shows the coil winder that I made which had adjustable tensioning springs on the feed spool shaft to keep the wire fed under tension so that the feed coil couldn't 'free-wheel' if I slowed or stopped the motor, the speed of which is controlled by a foot pedal. I won't go 'off piste' in this thread to bang on about the wider, which is a diffrent topic in its own right, and I've probably covered it in other threads, as well as in the BVWS Bulletin. Suffice to say that I wound on turns until the field coil former was full, figuring that I wouldn't be too far off the 2,000 Ohms needed. Not really critical as it's not an RF coil in a tuned circuit. 1,900 or 2,100 Ohms or whatever would do. (+/- 5%).

As the wire was solderable (the enamel acts like flux), I touched the wire with my soldering iron to tin it so I could check the resistance. had it been much less than 2,000 Ohms, I'd have insulated the tinned spot and added more turns - had it been more than 2,000 Ohms, I'd have removed turns, testing at intervals. Luck smiled on me that day - the coil was 1,997 Ohms! I fitted a lead out wire leaving the 38swg nice and slack and secured the lead out wire tightly so as not to fracture the joint.. As the original coil was wrapped in black plastic, I put a couple of turns of black Gaffa tape to finish off the coil.

I de-rusted the pole piece and sprayed it - see pic 3
I then fitted the field coil in place - see pic 4.
I re-sprayed the speaker body and fitted it back on the baffle board - pic 5.

Next, I tuned my attention to the main chassis - more of that later.