TRS-80 Model 12 crt substitution

On Mar 4, 9:34, Witchy wrote: I'll second that. Not only do CRTs not discharge naturally (unless they're in circuit with a bleed resistor), a disconnected and supposedly-discharged CRT may develop a charge if left alone. The original EHT can force electrons into the glass, and since glass is an excellent insulator, they don't come out again immediately when you discharge the tube. They *may* come to the surface slowly later, and give the CRT a significant charge of opposite to the original polarity. So leave a bleed resistor across a tube you plan to store for a long period (tip given to me by a TV repairman). If you're discharging a recently-used tube, don't use a simple resistor. The EHT on a CRT could be anything from 8kV to several tens of kV in a fancy colour tube, and most common resistors have a breakdown voltage of only 500-1000V. Besides, think about the power dissipation if you discharge a 25kV tube through a 10M resistor: 2.5 milliamps, but 62 watts. Sure, that 62W won't last long, but neither the tube nor your resistor will like it! -- Pete Peter Turnbull Network Manager University of York