winding a 20 tap coil

The switch on the left is the units selector and the one on the right is the tens. They are able to select from 10 to 109 turns a single turn at a time.As you can see I have an armature on the left hand switch. when I cut the bar I will make another for the right hand switch.

I put a little glue around the contacts on the bottom to help harden the board and seal moisture out. The screw has a terminal lug and spring to maintain contact while allowing the switch to turn without the wire twisting with it.

When it is wired I will have 10 turns with both switches in the center position. Moving the units switch CCW will increase the turns to 19. Moving the tens switch one click CW will give 29. Rotating the units switch CW will produce 20 turns. And so it goes. We can have 10 turns to 109 turns.

I used a paper towel core and a 1/4" fiber glass rod to wind the coil. You could use a pen or pencil with a straight shank. I simple wound 10 turns around the core and rod then nine on the core one on the core and rod etc. I pushed the wire under the rod with my thumb and put some Q-dope on the coil. After the dope cures I'll remove the rod and twist the loops to make a place for my connections.

Note: If you have no Q-dope use clear finger nail overcoat or varnish.