[miniman82]

Also agree that the CRT is not the problem. I don't recall, have you replaced all the original white inductors in the chassis? Every single one of those was bad in mine, even one that tested good at the beginning of the resto went bad after the electrons started whizzing around. Don't trust them, they are always bad!

Have you tested the 6BC7 resto tube, or done any subbing yet? The schematic doesn't have 'drive' controls listed, so I assume you mean the video gain pots on the little phenolic boards. What are your actual G1 voltages doing with the chassis driving the CRT? If the voltages are wildly different, I'd expect to find trouble in the output circuits of the individual matrix channels. Not saying they are going to be exactly the same voltage, but the fact that you're having to mod things points to circuit troubles. Sams has the inductors on each matrix output at around 5 ohms (L54/55/56 respectively), but they are typically wound on high value resistors because they make a quick easy former. If a coil has opened up in the matrix output, there could still be some voltage getting through on just the resistor. Food for thought, ohm them out to check.

This is very likely a DC voltage issue at the G1 terminals and not a video issue, the fact that the brightness isn't working correctly is a clue. All it does is set the DC offset on the G1's of the CRT, thereby varying their relative intensity. You could look at it as an adjustable cutoff control, if you like. Find your missing DC voltage, you'll likely find the problem.