I would think an electrolytic type capacitor would be the right kind. I don't have any idea as to the valve. I believe the distributer capacitor is of the electrolytic type, so give it a try. You may have to go bigger in value such as a you would find in a old tube radio power supply. Good luck and let us know how it works for future sufferers of this problem. BTW, these tpyes of capacitors are polarity sensitive. The case is usually negative or ground.

Six volt guy living in a twelve volt world