08-19-2016, 07:29 AM
Hi Rich,
This what I can tell about the coil. If there isn't enough turns on the tickler the oscillator will run at the high end of the band but die out at the low end. I would try adding more turns to the original form. Don't know if you counted the old winding but would guess about 30T would get you close. Needs to be wound near the bottom of the form as the old one was. Wire gauge is not really critical but should be 32G or less. If it quits oscillating at the low end you'll need to add a couple more turns. You can also try baking the coil at lot temp to remove any moisture. Philco in some of their service bulletins from that time frame would mention lowering the value of the cathode resistor, this raises the gain on mixer tube making it a bit easier to oscillate.
By adding your extra coil this add a lot of variables in to the circuit. Placement is critical and using clip leads to connect adds capacitance and inductance to circuit. Both of these factors could be the reason for your tracking issues. Using a tetrode tube to do both the mixing and act as the oscillator is a bit of a stretch but was the technology was at the time. By adding a separate oscillator tube makes the circuit simpler but add to the cost, and this was at the peak of the depression.
This what I can tell about the coil. If there isn't enough turns on the tickler the oscillator will run at the high end of the band but die out at the low end. I would try adding more turns to the original form. Don't know if you counted the old winding but would guess about 30T would get you close. Needs to be wound near the bottom of the form as the old one was. Wire gauge is not really critical but should be 32G or less. If it quits oscillating at the low end you'll need to add a couple more turns. You can also try baking the coil at lot temp to remove any moisture. Philco in some of their service bulletins from that time frame would mention lowering the value of the cathode resistor, this raises the gain on mixer tube making it a bit easier to oscillate.
By adding your extra coil this add a lot of variables in to the circuit. Placement is critical and using clip leads to connect adds capacitance and inductance to circuit. Both of these factors could be the reason for your tracking issues. Using a tetrode tube to do both the mixing and act as the oscillator is a bit of a stretch but was the technology was at the time. By adding a separate oscillator tube makes the circuit simpler but add to the cost, and this was at the peak of the depression.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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