HV current in a color CRT

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Rich Feldman
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Real name: Rich Feldman
Location: Santa Clara County, CA, USA

HV current in a color CRT

Post by Rich Feldman » Sun Jun 23, 2019 6:12 am

For years I had wanted to directly measure the HV current in a working color CRT.
Did it today and got a data point: 1.8 mA, with the screen at less than maximum brightness. That would be 45 watts, if potential is 25 kV.

First step was seeing a 27" TV being scrapped, _after_ making my HV-floatable digital milliammeter. TV has a plastic case, and CRT's mechanical binding and external aquadag are grounded through a single wire. But that's not part of the HV current's DC return path.

The TV (incl VCR and DVD player) is too heavy & unwieldy to safely handle alone. It filled the back of my car for almost three weeks, and was never taken out at home. This morning it passed a power-up test, with newly spliced power cord, so I removed the back cover and main anode "suction cup" connection. An exercise familiar since high school. Kids, don't forget to pull the plug and discharge the CRT before touching! You can safely let the vacuum out without breaking any glass, by punching or drilling through the thin metal anode bellybutton.

First power with Altoids meter in series resulted in snappy sparks, 'cause of inadequate insulation & air space. After fixing that, I got a nice image on the TV screen at the same time as a 018 reading on the meter. NTSC video input signal was coming by wire from the same camera that took these pictures. With camera inside car for the last picture, or at the instant of taking the picture, TV screen must have been darker (so less current draw).
With data point in the bag, I scampered to restore the TV's back cover and get to E-waste business before Saturday closing time. First removed the electronics package, including deflection yoke, in case it can help me light up a loose CRT of interest.

Was dismayed to hear that as of last week, CRT TV drop-off is no longer free; they wanted $25. Except at sponsored e-waste events, like one they'd had earlier the same day. :-( The new fee is only $10 for CRT monitors, and I asked how they tell the difference (since what I brought had no electronics except the one big tube). Lady took a look & declared "That's a TV". After some pondering: decided that I needed the car space, and am RIch, so forked over the fee & moved on.

Got to admit, color CRT's are a pretty spectacular technology. Did their half-century-long heyday see a billion units made?
Mike echo oscar whisky! I repeat! Mike echo oscar whisky, how do you copy? Over.

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Richard Hull
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Re: HV current in a color CRT

Post by Richard Hull » Sun Jun 23, 2019 7:01 pm

The world moves on, leaving CRT televisons and pile batteries to the junk piles of history.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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