Common items you passed up that turned rare when you wanted them

The method generally used on TV tubes of the period (and I don't see why monitor tubes would be any different) was something like : 1) Over-run the heater. Typically a 6.3V heater would be run at 8V or 10V 2) Apply a fairly high (200V-ish) +ve voltage the control grid (wrt the cathode), all other electrodes floating (no EHT applied either). This, combined with the overheated cathode, stripped the top layer of emissive stuff off the cathode, hopefully exposing a fresh surface. It worked will on some CRTs, on others, it totally removed the emissive material and you ended up with a totally useless CRT. But you've nothing to lose by trying it on an otherwise useless tube There was also a simple way to do an emission test. Again the only electrodes you used were the heater, cathode, and control grid. I think you ran the heater at the normal voltage and used the cathode/grid as a diode and measured the current flow with a fairly low (if any) +ve voltage on the grid. The higher the current, the better the cathode was emitting. Many designs for such devices have been published in the magazines. The lethal ones get the 300V or so by rectifying the mains (or in your case using a voltage doubler on the mains). More friendly ones used an isolating transformer or a oscillator/step up transformer from a battery. -tony