65 maggie

[DaveWM]

the video out tube is the 12XXX prob a 12BH7 or 12GNY etc...

when it gets weak the current drop thru the tube declines, the causes a lower voltage drop across the load resistors in the plate, this lower drop means the plate voltage goes high, this plate voltage is directly coupled to the Ks of the CRT, this higher than normal (195-200v) results is a bias in the CRT that cuts off the electron guns, this reduction it emissions from the electron guns reduces beam current and overall intensity of the CRT.

Now back to the orig question what is the K voltage EXACTLY. Also note if it varies with the brightness control (it should).

Remember if the voltages are correct then the ONLY reason the CRT is not as bright as the others is the CRT is weaker than the others (assuming all the voltage are the same on the others).