I did a lot of experimenting with various ballast configurations and ended up settling on a diode version.
Remember, the two filament strings are NOT equal in the TS-18 chassis.
81.7 VAC and 75.4 VAC for the two strings.
This is the prototype. More compact version coming up.
I built two capacitor version. The one with AC motor run caps was a bit too big to fit inside the original ballast tube.
This one uses Panasonic caps rated for 150 VAC, but not continuous duty.
They got noticeable warm from self heating after 15 minutes of use.
It also took several minutes for the set to fully warm up when using caps.
The diode version with themistor was a good compromise. Reduced heat, soft power up and set stabilized with in a minute or so. Also compact.
Cap version uses an 8uF and 10uF. Diode version uses difference series resistor values.
Here are the schematics.
Pure resistive. Gets very hot.
Least heat but requires bulky expensive AC rated caps.
Using diodes with resistors to fine tune drop.
Use two diodes in series for protection in case one shorts out.
