The heat sink was originally on the switching transistor for the High-Voltage board, but since the circuit pulls only about 5 watts for the B+ rail, the thing doesn't even get warm enough to the touch (the board can handle loads up to 45 watts, so 5 is almost a joke for it). I removed it from the transistor because the board fit in the enclosure better that way.
I had to put it back in the new position to work as a shield for the 6N21B tube, because the switching noise from the transformer was being induced onto that tube. The shielding worked perfectly well, being grounded to the common of the circuit.
A better solution would be adding a piece of metal attached to the chassis, sitting between the tube and the High-Voltage board's transformer, that wrapped around the tube a bit, for proper isolation.
It works as a proof of concept, at the very least. But now that I know, I can avoid this issue on future versions of the project, should those come to be. Wink wink
