10-26-2018, 04:51 PM
Oh no you found me [Image: http://philcoradio.com/phorum/images/smi...n_evil.gif].
I'm not quite sure why Philco decided to feed the screen voltage to the mixer and if amp thru that choke, It would seem much simpler just feed it from b+ that is over by the output stage. See the schematic for the model 60. It's pretty much the same - the choke.
If I was going to replace the choke I would try a resistor to mimic the choke. Value would depend the voltage drop (abt 175v). The screen grid current between is abt 6ma. If you do the math it ends up being abt 138K taking into account the 32K series resistor that is connected to the screen itself. In the real world a choke that measures any where near that resistance would be off the charts in terms of inductance.
Once a proper value resistor is connected you may have an issue w/bypassing the rf energy that's on the screen grid so adding a small value cap (.001-.005 630v) from the screen the chassis should take care of it.
I'm not quite sure why Philco decided to feed the screen voltage to the mixer and if amp thru that choke, It would seem much simpler just feed it from b+ that is over by the output stage. See the schematic for the model 60. It's pretty much the same - the choke.
If I was going to replace the choke I would try a resistor to mimic the choke. Value would depend the voltage drop (abt 175v). The screen grid current between is abt 6ma. If you do the math it ends up being abt 138K taking into account the 32K series resistor that is connected to the screen itself. In the real world a choke that measures any where near that resistance would be off the charts in terms of inductance.
Once a proper value resistor is connected you may have an issue w/bypassing the rf energy that's on the screen grid so adding a small value cap (.001-.005 630v) from the screen the chassis should take care of it.
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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