[emeritus]

The comment in #13 is noted. I can only say that the radio I mentioned in #4 was an ordinary domestic AC/DC table receiver (I forget which model: probably early post-war, not a DAC 90 but about the same size) wIth a tapped dropper resistor for mains adjustment. The section for 240V was open circuit and the radio must have been used for some time on 240V mains on the 200V tap, possibly accounting for its valves' low emissions. The very audible sparkler-like flashes were accompanied by audible crackling sounds. The volume, initially silent, got progressively louder with each application, and I stopped when no further increase was heard, about 5 or 6 applications of a few seconds each from memory. I had fitted a power resistor to replace the failed dropper section before doing anything else.