a new BBS...

Some old TVs in the UK had a metal-flared CRT, a metal cone bonded to the glass faceplate(screen) and neck. This flare fomred the final anode, of course. Downright unpleant, that flare was at EHT votlage when the set was on, and of coruse there are a separate filter capacitor (which if it heldf its charge meant that the CRT flare would belt you even when the set was off). I was specifically talking about the sort of monitors that are likely to be used with computers. It is not unherad-of for a colour monitor, at least not in the UK, to have a flyback transofmrer producing 8kV or so and a separate diode/capacitor votlage tripler module. The latter generally provides the focus supply. Some Microvitec monitors (commonly used with the BBC micro) and the Acorn Cambride Workstation's internal monitor (a Microvitec chassis, of course) were like this. I doubt you'll find valve rectifiers and the 'shunt stabiliser triode' in any computer monitor, though ;-) Well, provided you pick that 'ground' carefully. Clipping a probe on a handy 0V point and using the end to short the anode connector to ground mau well result in currents flowing where you least expect them!. I still dislike doing it. I rememebr -- well -- a TV where even the spark of connecting an EHT meter to the anode cap (earth side of the meter to the CRT ground contact) would blow a few transistors. Mains-derived EHT was used in the UK in some _very_ old monochrome TVs. A few, particulalry back-projection sets (White-Ibbotson???) had a semarate oscillator 9around 50kHz I think) driving a transformer/voltage multiplier circuit -- that one is high enough impedance to be no more dangerous than a flyback-derivied EHT supply. But direct mains EHT -- a 50Hz (or 60Hz) transfoemr and rectifier -- is low enough impedance that you want to keep well away from it. I think every raster-scan monitor you're likely to come across will have flyback EHT. It's cheap, and it makes used of otherwise wasted energy stored in the defleciton field. If you work on vector monitors, you can't do this because there's no regualr scan. You might have a mains EHT supply, or a separate osicallator/transformer circuit (the Vectrex gmaes unit does the latter, the transofrmer is essentially the same as a monochrome TV flyback transoformer, it just has nothing to do with the deflection circuit). I disagree. On delta-gun CRTs (unlikely to be found in colour computer monitors, but there are a few 1970's ones), the purity is set by ring magnets on the back of the youke (they look like the cnetring magnets on a monochrome CRT). The xtatic convergence is normally set by 3 permanent magnets on the 'convergence yoke' -- a Y-shaped thing bechind the deflection yoke on the CRT nexk with a separate 'blue lateral' unit behind that. Dynamic convergence is set by carefully controlled waveforms on the coils on the latter 2 yokes, there will be a dozen or more presets to adjust to set them up (and you have to do it if you move the monitor, turn it round, or anything that would affect the external magneic field as seen by the CRT). On in-line gun CRTs -- almost all computer monitors -- there are typcially 6 or more ring magnets on the back of the defleciton yoke. These set the purity and the static convergence. Dynamic convergence is set on older units (well by, again, careuflly controlled currents through coils in the yoke -- I've never seen this in a computer monitor though. In later models (anything after the late 70's, basically), there's no convergence _circuitry_ at all, the field produced by the defleciton yoke does the job on its own. You get the dynamic convergence right by tilting/wedging the yoke. I've read plenty of service manuals that confirm this... -tony