Newcomb Power Transformer TR-139

take-a-part on a big tube pwr supply xfmr,

Newcomb TR-139, has a 700 V-ac center tapped sec = 350 V-ac into ether a sold state rect or tube rect, whch will supply about 350 x 1.4 = 490 volts DC solid state, or about 450-460 after a tube rect,

done on a big 175 EI core with end bells, 8 amps 6.3 heater supply!

no ground wire on the shields which was weird,

we will rewind with a nylon bobbin and new wire and use it for a bass amp,

CJ, when you unwind one of these, how on earth do you count the turns????


Cheers

Ian

i unwind them on the winding machine which has a counter,

i did count turns by hand once on a UTC A-10, which was not fun as there were 8000 of those hair wire strands that broke if you looked at then wrong, 

> how on earth do you count the turns?

When you are not as fully-equipped as CJ, you can fake it.

Bring any winding up to about design voltage. Assume 117V into the "117" winding.

Before that, snake one (or many) turns of fine wire around the core.

Here we will get 0.52V on a one-turn winding. (May be better to take 10 turns, observe 5.2V, and correct to 0.52V per turn.)

Since modern walls are 120V-125V, we will observe 0.53V-0.55V per turn; but all other voltages will be high. ("6.3V" will be 6.7V, etc.)

The volt/turn is the same on *all* windings of a core. Knowing one, we can figure the others.

Volts per turn will run from under 0.1V/t on small cores to 0.5V/t on this monster and over 1V/t on kilo-VA house transformers.  That may be a guide when you do not know what voltages to expect.