Maybe a loose tube pin in the vertical circuits? Can you make the same thing happen if you tap the chassis say with a screwdriver handle? Might be the mechanical vibration that happens when you change channels rattling the vertical circuit.

Tried to tap on the chassis and some other components, but nothing.
The screen only blinked on with sweep a few times, can't seem to do it again though... the pins all seem fine in the vertical tube.

My other thought was, that when I ran out of paper caps,
I used a .033 film capacitor for the .035 paper axial cap, and two .0033 Orange Drops paralleled together for the .0068 axial paper cap.
These caps were right off the vertical tube socket,
I was wondering if that might be a problem, substituting those type?

That sub should be fine. Check for bad resistors, and check the transformers in the vertical circuit (usually a small one for the oscillator, and a bigger one to drive the yoke).

Thanks...
Do I test the transformers with a multimeter?

If that 3Amp fuse was in the horizontal circuit then I think you need to go with a 1/4Amp fuse there. It was a common hack repair to oversize the replacement horizontal stage fuse whenever it blew...Putting the flyback at risk in the future.

Thanks,
actually the 3 amp fuse is original to the circuit.

Got sweep!
Can't believe it, but after studying the schematic, I noticed I left out a 470 ohm 1 watt resistor from pin 9 of the vertical tube socket to ground.
Someone fooled with this set many years back, and replaced a couple of the electrolytics, but never took out the originals...they were all wired in together!

Anyway, when I pulled those caps out, the 470ohm resistor was wired together with a 100uf capacitor, and I just forgot to put it back in.

Now I have sweep, picture looks OK, when I can see it, BUT, I can just make it out...

If I turn up the brightness, the picture goes dark.

If I turn the brightness all the way down, and slowly turn it up about 1/4 of the way, I see a clear bright picture for only a second, then it goes just about completely dark.

Picture seems better the longer I run the set, but I can't brighten it.

The picture will zoom in very large, then disappear and go dark if I try to turn up the contrast or brightness past their halfway points...

Any thoughts??

Wondering if the picture going dark by turning up the brightness and contrast knob is a symptom of a bad CRT?

The picture zooming is a symptom of low high voltage, often caused by a bad HV rectifier tube.

That is called blooming. The first thing to check is the high voltage rectifier. Substitution of the tube is the best way to deal with it. That is a nice set by the way.

Thanks for the tips on the HV tube!
I would never have known...
I actually just changed that tube, a 1B3 I think, since the old one tested bad...

I do have another tube, but I am wondering since it is in the High Voltage cage,
is it safe to put my hand in there and just change it, if I'm careful not to touch anything else? I just had the set on for about three hours...

Make sure set is switched off and unplugged. Carefully remove the plate cap so as not to break any wires and remove the tube. You might have to try a few tubes to get one that works well in your set. Also make sure your power supply voltages are up to scratch so you don't have low B+ contributing to your problem. Those tacked on electrolytic capacitors will need to be tidied up.