1971 GE Portacolor H3 chassis color help

[zeno]

OK you set it to wormy & watch it. the worms go away & you
have to fine tune to get them back. If thats the case you have
tuner drift so ignore the rest of the set for now.

You can
1) clean the tuner
2) clean the 2 tube sockets. Pull the tubes, spray sockets then put the
tubes in & out a few times.
3) Get a NOS mixer / osc tube, thats most likely. If the RF amp is cheap
change that too.

good luck
Zeno