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Simple Hand-Powered Coil Winder

This project came into being as an accessory to my 1-tube Bloomberg radio. The depicted receiver uses an output transformer that converts a relatively low impedance of a small speaker (8 Ohm in my case) to approximately 8000 Ohm output impedance of the tube. The secondary must also pass the tube's DC bias current which in turn necessitates an air gap in the core. Back in the day, one could easily buy a transformer like that, (I'm sure samples are still available) but I didn't want this to become a search project. Since I wasn't after Hi-Fi quality, I felt I could easily make one myself, out of a junked small power transformer. All that is needed is a suitable donor "wall wart". Disassemble it without damaging it and then rewind it. To wind thousands of turns for the primary, you would need a machine. If attempted manually, the very thin wire could easily become tangled, develop kinks and eventually break. Some sort of mechanical aid is mandatory!

My version of a coil winder is very basic, all the wood came from Home Depot. It's very simply designed, construction is apparent from the picture on the left. The wooden base is made from 3.5" x 1.5" stock that is 8.5" long. The spindle brackets which double as bearings, are made of 3/4" plywood. All are 3.5" tall and 2" wide. The two brackets in the front of the machine hold the crank or "driver", the two brackets in the rear, mount the wire supply. Since I don't expect to disassemble the unit, I used a dab of wood glue and 2 wood screws for each of the four brackets. Because the unit will be used infrequently, wooden bearings will suffice. Feel free to improve upon my design, should you come up with a "deluxe" bearing version, please shoot me a link with a picture. Now that the brackets are permanently attached, the shafts need to be moveable. To ensure that they don't jump out of their sockets under tension, I cut the notches at an angle. Note: This picture was taken after I had finished the turns counter project and assembled everything. Thus, the display and the optical sensor attached to the lower right bracket were not part of the original design. If the machine is meant for winding only a small number of turns, the counter may be omitted altogether.

Here you see it as viewed from the front. My machine is quite small (and my project table is small too) so the counter was mounted inside the base. The black object in the front of the base is 3mm power supply socket.

Both shafts were fabricated out of 4mm welding rods that someone had thrown into the recycling bin outside. I cleaned the stuff off the rods and threaded them. 4mm diameter seems strong enough for my transformer sizes. The rod to be used in the front I bent into the shape of a crank. To make sure the crank doesn't develop sideways play while being turned, I used two brass round pieces, both threaded. The one on the right later came to hold the optical sensor vanes.

In order to use the machine with a given coil former, I first shape a wooden block so it fits snugly into the former. Then I drill a 4mm hole longitudinally through the block so slides on the shaft with ease. To secure its position on the shaft I use an aluminum nut, it presses the wood against the brass on the right. Finally, all "bearing" areas got a few drops of ordinary motor oil each to lubricate the action.

A close-up of the crank and counter sensor.

Rear shaft. It's threaded from end to end and has two large nuts. These clamp the wire supply spool to the shaft so that the shaft, rather than the spool rotates.

 

Last but not least, when the next transformer winding project rolls around, I may upload a video of the machine in action. Stay tuned!

Good winding, 73 de Brian.