Slow fades then slow brightening of px often the
filaments loosing volts. Just see if they are changing.
HV rects were about the only thing that went on them
in the olden days, sometimes yearly. IIRC they used
a 3A3 & some times a 3CU3 or 3DB3 ?? And dont
neglect module contacts, usually can smoke them out
with light poking & tapping.
73 Zeno
