[Arran]

I found the schematic on Nolstalgia Air, it's a series string transformerless set, you can add a dropping resistor if you want but the value isn't as critical, some people add them and some do not, normally the drop across a good selenium rectifier is about 4 volts or so whereas a silicon one is .7 volts so it likely won't be that much higher. What normally happens is that the internal resistance of selenium rectifier increases with age to the point that it can't pass enough current to operate anything, it sin't common for them to short out and smoke unless they are overloaded in some way. There is already a voltage divider resistor in there I see, which looks like a candohm type, this should be checked for open sections. If the selenium rectifiers are defective I would replace them with diodes and try it out, if the voltage is considerably higher you can add a resistor ahead of the voltage divider. Another way to replicate the drop across a selenium rectifier is to connect two or three diodes in series, basically this is what a selenium rectifier amounts to is a stack of diodes in series, but made out of dry metal plates instead of a silicon crystal.
Regards
Arran