Is 100 +/-20 micron bridgeable by a tin-whisker? This minimum insulation
gap (under x30 visibly compared with a .08mm diameter wire) is between
the pad for that control pin and one of 4 grounded pads for a screening
can, not used in this amp, but was used on the scrapped amp. The
remainder of the ring insulation is about .3 mm. Could a flux or flux
remover associated with PbF induce a whisker over 100 micron ?