HV pix tube Current

[hi_volt]

I used to design high voltage power supplies for high resolution CRT displays, and worked for Rantec back in the 80s. If you look up the specifications on most CRTs, they will provide a recommended maximum anode voltage and a rated beam current. For most of the monochrome tubes, the beam current will run from around 200uA to maybe 600uA at full brightness. For a color CRT, the beam current can run up into the range of 1mA to around 1.5mA. At 25kV and 1mA, there 25 watts being dissipated in the CRT, which can be quite significant. On some of the small heads-up displays we designed power supplies for, the screen was only 6" wide, and if the brightness was turned up high enough, the shadow mask would heat up and actually distort, the effect of which which you could see on the screen. Also, if you run a small CRT like that this hard and happen to lose horizontal and vertical sweep and just have a dot on the screen the energy density was enough to burn a hole right through the CRT glass in about 2-3 seconds.