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The cathode current can be measured by unsoldering the ground lead from the cathode pin of the h output tube socket then connecting the meter positive current terminal to that pin and the meter negative to ground (sometimes you should put a .47uF cap parallel to the meter ). The current will be in the neighborhood of 170mA to 230mA DC. make sure your meter has a 500Ma DC scale... I'm not familiar with your meter so check it's specs/manual. Also it is preferable to use an analog darsonval movement meter to a digital meter... it is a high frequency pulsed DC current on the cathode. An analog meter will average it well and be the same instrument that Sam's and the factory used to measure that. Some DMMs may get confused by non constant DC... I have not had that issue, but since I have an analog meter I use it instead of my DMM.... it is better for adjusting the efficiency coil for minimum current than most DMMs since it will show you minute changes that a digital display will hide in rounding to it's smallest digit. One recommendation when you're done measuring the cathode current connect a new wire to the cathode pin, run it above chassis to a good spot to ad a fuse holder, ground the cathode thru a 1/4 amp fuse. Doing this will help protect the flyback from excessive current, and the fuse holder above chassis will also make a convenient current test point for future measurements... all you will have to do is remove the fuse and connect a meter across the holder terminals.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 Last edited by Electronic M; 11-13-2018 at 01:51 PM. |
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For the record though how can i set my meter up to look at the |
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Look at the what?
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
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Do"h
I want to look at the overall ac current draw the set is using. I checked my fluke meter and it tops out at 320ma so an analog dc milliamp meter is on its way. |
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All that said there is a way to indirectly measure the AC that set uses with your present meter (assuming it has an AC volts range) get a 5W or higher, 1 OHM power resistor place that resistor in series with one leg of the cord (can hack up an extension cord to do this (and make a universal adapter) ) then with the meter in AC volts range measure the voltage across that resistor...You can then compute the approximate current using ohms law: I=E/R= measured voltage/resistance...Given resistance should be 1 OHM that means measured voltage should be approximately equal to the current flowing. The accuracy of the resistor, the accuracy of the meter, where you connect the meter along the wire will all introduce some error to the measurement, but it should give a decent approximation.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
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Youve been really helpful so far. Cleaning out the hv cage and all the leads. I swore this hissing noise came from the back side if the cage. It will be a while till I get that dc milliamp meter in the mail. One thing i forgot to mention is that one of the power resistors has been replaced on the chroma board. Also Ive been told theres a trace along that board that tends to fail. Fortunately mines in good shape. All ive done to it to add on is replace a few e caps and reflow the ground stags. Some have mentioned hard wiring the ground with a wire. To touch up on your earlier post the ctc 25 does use a cup ontop of the flyback where the plate cap of the hv rectifier sits inside. I will wrangle up a few and see if it helps next time i power it up with a ammeter telling me what the cathode current. If any of the wire insulation is at fault from breaking down (and this IS a high hour set) what would be a good replacement? I imagine regular old heat shrink tubing wouldnt be good enough for the 24kv.. |
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