First off keep in mind what a Portacolor is & isnt. It was built to
sell at $220, later $199. As a rule everything was the cheapest
possible with the lowest parts count. Brand new they "worked"
and thats it. Do not expect perfection from it, GE didnt.
GE stands for "Good Enough" dont you know.....
One thing we found was a PC, especially a first gen like yours after
a few yrs needed a lot of work If we changed one low level tube at a
time you could see improvements with each one. Bad news is
compactrons cost $$ even in 1970. So they were fixed to "work"
again & no more.
Notes
Audio. Put it last. Buzz is detector stage, hiss is audio IF stage.
Vert collapse not normal.
"Blooming" change in pix size probably normal for this set. It is not
highly regulated like in expensive sets.
Tuners have 3 bands. VHF low ( ch 2-6) VHF high ( ch 7-13) &
UHF ( ch 14-83). When the UHF is used 3 things happen.
1) UHF tuner gets power. 2)The VHF osc gets turned off.
3) The RF amp & the mixer in the VHF tuner are turned into two more
stages of IF amps.
So you can get very different performance on different bands with weak tubes. But it can give you clues.
BTW they will usually test good.
IMHO your best next step is to get a good stable source of a color pix
pref a DVD with an RF out.
enuf fer now
73 Zeno
LFOD !