Good question! This is safer to tell and ask. This is cardial rule here at work, I always make sure I can see the plug is visible and is clearly goes to that that unit I'm working on. Also there is few capacitors still charged by the way. My discharge "tool" is basically two clip cables and sand block resistor of big wattage like 10W to 20W, 180 to 220 ohms is PERFECT for both charged caps and HV discharges. I usually discharge any caps that are marked 35V or higher by touching and holding for few seconds with pair of that clips via that sand block resistor, there is few caps that is so BIG it has heavy pins, I leave them clipped for few minutes, they leak away so long. Reason I use that resistor for HV discharge is to cut down on current (damage can happen because the internal dag coatings can be burnt off around the anode button or blow a component. The dag ground is dead easy to find. It is the bare braid cable sketched across the CRT's bell touching the dark grey dull coating (dag). I always clip to that ground strap across the back side of CRT bell via same resistor and clip that to a small worn flat head screwdriver with plastic handle. Carefully wiggle this under that HV suction cup and you're done the instant screw driver tip touches that HV prongs. You will hear few crackles or quiet snap using resistor. Without it, you get a loud scary SNAP! Keep the discharge tool away the board or wires. HV can jump anywhere where there's easier path to take. Highest HV typically seen is about 30KV in projectors, big CRT TVs (32, 36 and even 40")., somewhat less in monitors. Finding the dag ground is MOST easiest and safe than sorry. I don't hook that ground end to the chassis ever. this is not always direct connect to the dag ground. hard to tell which is hot or cold even it is not that direct. Also another reason to be safer because components are protected only using dag ground to leak that HV. I always do this to any CRTs every time if I must get HV suction cup off. After discharge grab hold of the edge and fold back, gently push one tine of the anode clip to get it over the lip of the anode button. Clean both surfaces surrouding anode button (windex and alochol because the red "paint" comes off with actone and beyond for few inches and the suction cup (actone) then apply thin line in a circle around the button where suction cup will touch with dielectric silcone grease before clipping that HV lead back on, auto shops stocks this slimy grease in a tube of any size. I've seen HV sneak past the layer between suction cup and the CRT bell surface when a guy touched the edge of suction cup with screwdriver clipped to the dag ground. Blue arc with a some "crack!" He looked surprised and that one didn't have grease, was original dry install (typical in many CRT stuff and I don't like this way because of this HV leaks that could occur. Also HV burns through materials when it breaks through. Often looks like a faint pinhole (found by flexing and pullng) in flexible insulation. Even a tiny pinhole (like a period of a sharp pencil) in the flyback, the worst ones usually looks like someone blew out a side out and charred. Once saw a wisp of "hair" those actual super fine magnet wires for the HV winding got blown out of the flyback's casing giving it a bit of a tuft sticking out of axial crack running around the flyback's case. HV can be destructive if left loose to run amok in the chassis. :-) Snap crackle pop zzzzzzzzzzt or touch you. OW! or fling you off (secondary injury). For 2 and half years, I have YET to be bitten by HV hit but someday I may! But I have been buzzt'ed or shocked several times by the charged caps or high voltage stuff like 100Vto 300V (to me any shock is like a buzzt than a "zap") Had got on high freq 1.2KV ac (15.7KHz) kinda gives you a burning (stinky) fine trickle but still a fair "ow" rather like a brush of soldering burn. I was told HV hit is like mule kick. But I wonder what others who did get that hit felt like? Oh, I had been "shocked" by a experiment low level HV generator (felt like powerful static zap) but not that powerful at electronic class years ago. At science museum once saw a very tickish student girl walk off lexan platform by the big sphere HV generator depsite tech's warnings as she stepped off a looong 2 feet long arc hit her but she only did make short yelp without jerking or jump. Wow but I wondered why she didn't "bounce" or jerk or fling a arm or leg when HV hit her when her muscles spasmed. That 2 feet long HV arc must be really packing of power. :-O Cheers, Wizard

Merely in the interests of spawning another near-infinite regress on electron fundamentals... NO, it specifically had VERY LITTLE POWER, though a lotta voltage. P = E * I E= voltage, I= Current Probably as much POWER as a nine-volt battery or two. If it had much more, it would have been an unsafe display, as it's S.K.O.P. (*) to either not see, or ignore, or spite, safety warnings, and kid science museums certainly know that! * Standard Kid Operating Procedure. I speak from experience. (Hammering loaded cartridges 1 ohm 1W resistor on car battery cut plugged-in extention cord w/scissors on a dare (do it quickly) burn worms with 500V 100ft coil wire on car battery fun w/ignition coils fun with Hg fun with molten metals acids gravity 'parachutes' largest anything smallest anything smelliest anything crush vacuum tubes under foot surplus photo chemicals gasoline auto parts tensile strength of treetops...) tomj

On Wed, 26 May 2004, Ashley Carder wrote: No prob - been working on the damn things (TVs etc) for more than 40 years now.... and I've been hit a few times with Ultor HV - like most high voltage/low current supplies - there is usually not enough power there to do much real damage, what usually happens is you get zapped, and then damage the device / hurt yourself in the ensuing reaction - it's quite startling and painful so one tends to 'jump' - once I put my butt right through the neighbor's drywall in their living room when I was in Jr. High - took all my summer money (including my labor charges to them) to have it repaired and painted... ;{} maybe *that's* why I hate TVs so much! 'Wizard' has responded also to this thread with much more detailed info - I don't think you'll have to worry about discharging the power supply caps in a VT52 - there's no 'medium' voltages until you get to the HV supply. When he refers to 'dag' he means the outside coating (a dull black matte finish) called "aquadag" that is the conductive outer layer of the CRT - the front periphery of the CRT ought to be clamped to a frame to hold it in place - you can use this frame/clamp assembly to ground your discharging screwdriver. Somtimes there will be a thick uninsulated metal braid going from this peripheral clamp to the chassis somewhere - this can be used as a conveient place to attach your discharging wire. The ground prong of the power cord (the longest, round pin of the three) is always the green, or green/yellow wire in the power cordset, and will always be attched to the main ground point in the device. You may or may not hear a snap, or see a small blue flash when you get the tip of the screwdriver close enough to the anode connection - it depends on how well the CRT in the terminal is retaining it's charge. So combine both our narratives and you should be just fine. Only please do remember: Power cord UNPLUGGED and visible to you before starting the work. Cheers John

Please don't do it this way -- without some kind of limiting resistor. When the screwdriver makes contact a high current will flow which (a) can damage the CRT (it can burn the connection between the internal final anode coating and the connector socket) an (b) can induce currents in other parts of the instrument and blow semiconductors all over the place. It's proablt OK to discharge a CRT this way if you're going to throw it out anyway, and if it's removed from the device, but even then I'd not risk it. Use a limiting resistor! Considering the shaft is connected to ground through a very low resistance in your set-up, what's the harm in touching it ? And are often only rated to 1000V. That's enough for working on live mains (which is where I use them), but CRT anodes run at 10-25 times that voltage. I am not sure what the breakdown voltage of insulting tape is (yes, I always call it that!), but it's not that high. I doubt that a layer would stand 10kV (which is what you're asking for here, at least on a colour CRT). -tony

On Thu, 2004-05-27 at 17:04, der Mouse wrote: I'm sorry, but this is all very silly. A meteor could smash you dead too, it's just not a real worry. You have actual control over the puny alligator clip. Live large! I knew this thread would get out of hand...

On Fri, 28 May 2004, ben franchuk wrote: No; warning against using meteor clips during an alligator shower is out of hand.... Cheers T. Geisel

On Fri, 28 May 2004, Tom Jennings wrote: They aren't called "nerds" for nothing. -- Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org [ Old computing resources for business || Buy/Sell/Trade Vintage Computers ] [ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]

Yes. Most small resistors are only rated for 300V or so, so you need 100 of them in series, really. Try using 100 off 100k or 1M :-)... High voltage resistors do exist (I've used some rated at 7.5kV, which means you only need 4 of them), but you need to be careful how you mount them. If you do a lot of work on CRT based stuff, you should get an EHT proble. It's really just a high-value HV resistor, either with a built-in microammeter in series, or as part of a potential divider to use with your DMM). It's good for discharging the CRT, and it's useful for checking the EHT is there in the first place. -tony