08-31-2020, 05:45 PM
I once did a Grunow oscillator coil, two bands, two layers. There ws no hope of finding a replacement, overall a very fine console radio, I have forgotten the model, it had a BFO as tuning indicator instead of an eye...
I drew the coil as a flat object on a sheet of paper, marking the perimeter as degrees. I located all the lugs, direction of the turns, layers position of turns, layers and all the tiny holes the wire went through to which lug...
I stripped the form beginning with a heat gun then solvent. Jigged the form in a Morris winder an gently unwound to confirm the turns. The washed the form with acetone. The forrm was then given a hot dip in bees wax, placed in a vacuum dome (homemade) and a vacuum pulled with a hospital salvaged pump, moisture came out of the form like foam. When all the bubbles went away I pulled the form out of the still melted wax, that left a thin film of wax, thus, the form was tacky so windings would not slip around. Put the form back in the Morris and wound as instructed by the drawing A thin layer of PEET plastic film wax stuck to the primary with brushed on hot wax, then the secondary wound, all wires soldered, then the form went back into the hot wax and again the vacuum, more bubbles but not much. The layer of wax was very thin so I though I would like to do a thick dunk, like Zenith coils... So I let the form with windings cool then dunked the coil very quickly once, then again after waiting a few minutes. The result was a nice thick layer of bees wax to keep out the moisture...
I installed into the radio and it played near perfect with but a 1/4 turn on the trimmers. Happy, happy.
If I were to wind another I would use the same technique. The advantage was I could walk away for days and everything was on the paper...
Chas
I drew the coil as a flat object on a sheet of paper, marking the perimeter as degrees. I located all the lugs, direction of the turns, layers position of turns, layers and all the tiny holes the wire went through to which lug...
I stripped the form beginning with a heat gun then solvent. Jigged the form in a Morris winder an gently unwound to confirm the turns. The washed the form with acetone. The forrm was then given a hot dip in bees wax, placed in a vacuum dome (homemade) and a vacuum pulled with a hospital salvaged pump, moisture came out of the form like foam. When all the bubbles went away I pulled the form out of the still melted wax, that left a thin film of wax, thus, the form was tacky so windings would not slip around. Put the form back in the Morris and wound as instructed by the drawing A thin layer of PEET plastic film wax stuck to the primary with brushed on hot wax, then the secondary wound, all wires soldered, then the form went back into the hot wax and again the vacuum, more bubbles but not much. The layer of wax was very thin so I though I would like to do a thick dunk, like Zenith coils... So I let the form with windings cool then dunked the coil very quickly once, then again after waiting a few minutes. The result was a nice thick layer of bees wax to keep out the moisture...
I installed into the radio and it played near perfect with but a 1/4 turn on the trimmers. Happy, happy.
If I were to wind another I would use the same technique. The advantage was I could walk away for days and everything was on the paper...
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
