Vivitar thyristor flash manual power control mod

A little over a week ago I learned that I can very easily modify my Vivitar 3500/35-D flashes to have manual power output control. Previously I tested the different settings on the flash. To give me full manual control I have replaced the photo resistor with a potentiometer. This should work with all Vivitar flashes that use a photo resistor to adjust light output. This mod is quite easy and only took about 15 minutes the second time I did it. The 3500 has a separate module where this circuitry is housed. I know some Vivitar models are one unit, so be aware that flashes have a high voltage capacitor in them and you can shock yourself.