[TinCanAlley]

Originally Posted by old_tv_nut

Something's wrong with your measurements - either you are not measuring G1, or something else is going on.

G1 voltage higher = more brightness. Cathode (K) voltage higher = less brightness. It's mainly the difference between cathode and G1 that controls beam current, so you have to measure both to figure out what's happening.

These voltages *should* change to a predetermined value when you go to the setup mode, so that you can set the G2s for proper cutoff; then when you go to normal, the signals on the cathodes and G1's will produce the right colors.

This is what I got out of a book on CRTs.

"The control grid (G1) controls the brightness of the CRT. It is generally
placed directly on top of the cathode. If there is no voltage on G1, the
electrons can flow freely from the cathode. If there is some negative voltage
on G1, the electrons from the cathode are repelled somewhat, and the screen
appears darker. The greater the voltage on G1, the darker the screen becomes, because more electrons reaching the screen equals a brighter image, and less electrons hitting the screen equals less brightness."

I'm attaching the CRT section of the schematic. If I have the G1 information incorrect, I need to know. My understanding is pins 2, 11 and 6 are the G1s. I'm also attaching a pic of a chart from a CRT tester manual.