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| Current from Discharging 50Kv Color CRT |
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| jzx:
But use a resistor rated for 30kV. |
| jzx:
--- Quote from: wasedadoc on September 03, 2024, 06:59:04 pm ---The replacement had seen some previous use but had been in its protective box with shaped internal packaging for years. --- End quote --- Could it be charged by rubbing against the packaging? |
| CaptDon:
There is no point in the wire being insulated to kilovolt or more levels. Worthless advice. First off, the cable SHALL be grounded to chassis or the factory designated point when discharging a CRT of a set that was recently in operation. Secondly, what good does 3KV insulated wire do when you would have 25KV on it in the event you were stupid enough to not connect the ground clip? Any off-the-shelf stranded 300 volt rated insulated wire between 14 and 20 gauge will be absolutely fine. A discharge without a current limiting resistor could possibly damage the connection between the aquadag and the cup. I have never heard of any damage and to my knowledge in tens of thousands of intentional discharges at my father's T.V. repair shop I don't know of any short or long term CRT failures caused by hooking a ground lead to a long thin screw driver and discharging the CRT without current limiting. Most often however, we preferred to discharge with the Pomona high voltage meter which by nature of its physically long internal high voltage resistor limited the discharge current and any potential damage from a high current arc. Some manufacturers specified where the return lead MUST be connected for discharging and I believe it was to the ground straps wrapped around the outer aquadag of the CRT. |
| andy2000:
The highest voltage I've heard of on a home TV is 31.5kV, on large 35"+ CRTs. Most are closer to 25-27kV. The same goes for typical projection TVs. They usually run at about the same HV as a color TV, which is a lot for a 7" monochrome CRT. While I have heard of projectors using 40kV and more, I believe those were all really early (1960's) professional systems, not something you would find in the home. I'm not sure where this concern about damaging the CRT with the discharge current came from. I've been working on CRTs for many years, and read many books, and service manuals. None have ever said one word about potentially damaging the CRT. There just isn't enough energy there to cause that kind of damage. What they do caution you about it zapping the electronics with the HV discharge. The safest place to ground the HV to is the grounding strap on the outside of the CRT since that directly connects to the outer plate of the capacitor formed by the coatings on the CRT. If you have a HV probe, by all means use it to gently discharge the CRT, but if you don't, I guarantee you won't hurt the CRT by using a jumper wire. Buying a HV probe just to discharge one CRT would be a pure waste of money. I'm not sure why people obsess over CRT discharging. Yes, you need to do it if you're going to unhook the HV connection, but it's not a big deal. It's not even close to the most dangerous thing in a CRT TV. I would be more worried about the mains, and B+ voltages in the power supply, dealing with sets that have a hot chassis, flying glass if you break the CRT, or back injuries from lifting a heavy TV. |
| wasedadoc:
--- Quote from: jzx on September 04, 2024, 12:13:44 pm --- --- Quote from: wasedadoc on September 03, 2024, 06:59:04 pm ---The replacement had seen some previous use but had been in its protective box with shaped internal packaging for years. --- End quote --- Could it be charged by rubbing against the packaging? --- End quote --- No. |
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