GE sets of this era used to get bad doubler caps. It usually gets extreme
but yours may be just starting. The main filter cans were not a
problem on them ( 40 yrs ago !). Since 'lytic cans rarely short try
bridging apx 80 mfd across the doubler cap & see if it gets better.
Running at 50 cps in theory requires bigger caps but there is some
room there.
BTW bridging electrolytics is an old trouble shooting technique.
It can save you time & $$$. Also give you a look at the pix to see
if you want to go further with an old set.
BTW2 If you change a doubler cap be SURE you use one rated at
the same or higher temp.
73 Zeno
LFOD !