06-05-2017, 09:45 AM
No not necessary, you can filter using just caps and resistor. If you look at more modern set like ac/dc set from the '50s there's no inductance in the filter. Just as a guess if you didn't increase the size of the caps your probably looking at 5-8H to replace the field coil in terms of inductance. The series resistance isn't very critical in this circuit. Where it is critical is when the field coil is connected to the HV center tap back the chassis gnd. In this case the fc or choke does two things filters 60cy hum and develops negative dc voltage used for biasing. The fc dc resistance determens the amount of bias. Circuits wired with the fc or choke in this fashion are known as negative lead filtering.
That's part of the long answer to your question. The short answer is to use a 1700 ohm 25w resistor in place of the fc. Actual dissipation is about 15W but nobody likes a flaming hot power resistor. Remove the .05mfd that is across the fc it's used to resonate the inductance to the fc to 60cy and will just couple hum across the replacement resistor. Good practice sez to limit the input cap below 40mfd so 33mfd is good and while your ordering go ahead and replace all 3 of them with 33mfd @ 450v.
That's part of the long answer to your question. The short answer is to use a 1700 ohm 25w resistor in place of the fc. Actual dissipation is about 15W but nobody likes a flaming hot power resistor. Remove the .05mfd that is across the fc it's used to resonate the inductance to the fc to 60cy and will just couple hum across the replacement resistor. Good practice sez to limit the input cap below 40mfd so 33mfd is good and while your ordering go ahead and replace all 3 of them with 33mfd @ 450v.
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
