[Arran]

I think I know what may have happened, you may have miswired the negative end of one of the filter capacitors, probably the input filter capacitor coming off the rectifier tube and ahead of the field coil (filter choke) of the speaker. In many pre war radios the input filter capacitor has a floating negative end that is connected directly to the center tap of the power transformer, the output filter cap is connected to the chassis, and there is a large wire would resistor or series of resistors between the two capacitors on the negative side. I could go into a long explanation of why they did this but the simple answer is that they wired the power supply this way to provide negative bias for the tubes.
Regards
Arran