History of the Spot-Killer circuit

[old_tv_nut]

I suspect this will be hard to identify, since some designs naturally discharge the high voltage when the set is turned off and do not need a specific spotkiller.

Regarding oscilloscope burns, these were very common in the old scopes like the Tek 535. Later, thin-film phosphors that were much more burn resistant were developed, although they may not have been suitable for all applications.
I encountered these when working on the "EVR" flying-spot video player. The old type of phosphor would be burned badly if the vertical sweep failed, but the thin-film (which was proposed to us by Tektronix, but too late to get into production before the project died) could sit with the vertical collapsed for minutes at a time with almost no burning.
The flying spot raster was double-height during normal motion play, in order to follow the continuous film motion. For still images, the raster collapsed to normal 3x4 ratio, but this meant the center half of the motion-play raster would get burned in and then show as a dark horizontal band in the center of the screen during normal play. The player included a random centering shift when going to still mode to blur the burn band.

I believe some scopes may have had anti-burn circuits of some kind - can someone verify?

[wa2ise]

I think all you really needed to do to build a spot killer was to bypass to B+ the brightness line feeding the CRT grid 1. This in sets that fed the video into the CRT cathode. SO when the set was turned off, the B+ would collapse, and the bypassed grid would be pushed very negative, cutting off the cathode. and the cathode cools off by the time the time constant of the cap and resistances around it bleeds off charge.