Wow that jug looks strong ! Rare to find a '70s Sony with a good
one.
Purity looks like a few correction magnets fell off. They are small discs
sometimes on a plastic piece. They are taped to the CRT bell as
needed. You can use refrigerator seal gasket magnet for a sub.
Put near blotch & rotate & or flip over to get correction then tape down.
Had a few of these with cold joints at the SIF-DET-PRE AMP IC.
after that probably a 'lytic causing your audio woes...
Good Luck
73 Zeno
LFOD !