duga3 wrote:To achieve best blacks on CRT you need to lower the contrast to the point where black signal produces 0 cd/m2.
The contrast setting (actually RGB gain) should be maximised to a point where no clipping artifacts appear (i.e colored trails can appear going right of white details, the cathode amplifier transistors saturate and won't return from it immediately), it is the brightness setting (aka DC offset - black level) that needs to be toned down but also to a point where the video path won't clip, once that is done the acceleration voltage (G2) needs to be adjusted, which is often only possible with a screwdriver, and while at it the focus settings should be adjusted too (preferably in highest resolution and refresh rate you plan to use). Both of those often drift with time, or rather their preset value no longer corresponds to state of the tube.
The higher the acceleration voltage the better sharpness you can get and the brighter the image can be (dynamic range increases) but if the cathodes are worn enough the video amps no longer can drive them to cutoff state (no electrons pulled from the surface) and you get tinting of black or other dark colors (in color combination of weakest cathodes). This will also get you more headroom in the black end, so you wouldn't need as much additional correction by other means.
Sometimes it is possible to control the anode voltage too (couple tens of kV, depending on tube size) but it should be left alone without access to means to measure that voltage. Raster size and brightness will change, lowering voltage will expand the raster while image dims and increase will shrink the raster with increase of image brightness. Lower voltage pulls the electrons less hard and they can spend more time in the deflection field and thus reach higher deflection angles and so raster expands in size, they also slam slower into the phorphors and produce less light and less soft x-rays. X-ray production happens *always* but the amount of photons is very low (even on special xray production tubes, less than 1% of the electrons turn to x-ray photos) and all of them are absorbed by the glass. Here's some very good reading material on that matter : http://www.tmeeco.eu/BitShit/CRTemissions.pdf. Too high anode voltage can result in various breakdowns and any dirt etc. might cause a conductive path from anode cap to deflection coils or nearby aquadag and in worst case the thin glass where neck is will experience dielectric breakdown and vacuum is lost.
All of this should only be done after at least 15 minutes of powering on the monitor (staying in standby won't count, it must be out of standby). Most of the tubes are fairly worn by now, cathodes will take a longer time to reach proper optimal conditions for their wear level. Electronic parts also require some warmup time but generally not very long. It is normal to see raster size change slightly after 10 minutes of use, part of it is caused by DC resistance change with temperature of various components such as the deflection coils and various transformers, slightly altering the current/voltage profiles compared to cold state, temperature coefficients of active component play a role also. My main monitor requires about 20 minutes until lower end no longer crushes and raster reaches final size.
Things lighting up in a black screen in presence of a bright spot (regardless of color) is caused by secondary emissions, electrons that get absorbed in the mask or grill will make the mask or grill create their own electron emission which creates faint greyscale (since those electrons no longer target specific phosphors) halos around the spots with greatest emissions. This is the primary limiter of contrast on a CRT and a similar thing happens on OLED panels too but there it is purely caused by light bleed and reflections inside the panel. Ambient light also has ability to make the phosphors glow but that's but that effect is also faint, you can test for it in a dark room : Close your eyes, flick light switch on and off, then look at the monitor, you should see a faint glow that will last tens of seconds. You need to have your eyes adapt to darkness first, which will take several minutes.
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On topic, I use a CRT monitor even with modern stuff. Immediate response time, great contrast and color, variable refresh rates and resolutions still play a big role for games. 2560x1600 (but only at 60Hz) was also fun to see, and much to my surprise normal text was still readable... http://www.tmeeco.eu/BitShit/HighRes0.JPG - http://www.tmeeco.eu/BitShit/HighRes1.JPG 🤣
EDIT: Looks like my post will belong elsewhere too 🤣
