Jamie t wrote in message
...
N_Cook wrote:

Curiouser and curioser. There is a black "washer" between tag and pcb
pad.
Undoing a bolt this was a standard black nylon TO3 mounting insulated
washer
but on the underside. So instead of bolt head, insulator washer, TO3
flange,
mica, heatsink, pcb it is bolt head, flange , mica, heatsink, pcb, pcb
and
trace, TO3 insulator upside down, solder tag, star washer, nut. Flange
is
same thickness as pcb and nylon insulator is only long enough to half
penetrate the pcb so what advantage ? or cock-up?


Some times if you were mating with the board copper, they used different
types of material to prevent erosion.

Jamie




But an insulator ? I reckon cockup , myself included. I should have said
plain cylinder insulator set solely in the heatsink hole rather than necked
washer under the head, or there would be no electrical connection to the TO3
flange .