Motorola VT71MB-A restoration

[bandersen]

Thanks guys. Currently, I'm working from home so I still have some energy left after work for these old sets. Much better than sitting in traffic

Last night I did a little ballast experimenting based on the ideas in this great thread
Left to right - Clarostat replacement, JFD OEM, Amperite replacement and homebrew with capacitors.



I also made one with diodes and both work just fine. The basic trade off is that the capacitors run cooler, but are bigger and more expensive than diodes + resistors.
Also, adding 100K bleeders as Reece suggested is a very good idea. While tinkering with the caps, I got a heck of a spark when a tool shorted one out long after power had been turned off.
Glad it went through the tool and not me


Also, note that the two filament strings are not equal if you added them all up - 75.4 vs 81.7 for a TS-4J late. That's why I have different resistor values in series with the diodes. I also designed these for 125 VAC rather than 117VAC.