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In Reply to: RE: Can you post a schematic? (nt) posted by Tre' on March 18, 2017 at 10:27:42
I do not have schematic software but here is what it is. Full wave damper diodes to a .33 uf cap to 30hy choke to 2uf cap to 10hy choke to a 12uf cap to 5hy choke to a 100uf cap to interstage transformer to plate.
Pretty standard power supply. Caps to ground chokes in series. This is to one tube only so current should be the same from beginning to end.
Did you add the resistor in series with the choke or in place of the choke.
It was put in series after the last cap. Everything else is the same.
The resistor lowered the voltage to the tube so the current decreased.
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"Still Working the Problem"
"The resistor lowered the voltage to the tube so the current decreased."
I think he's saying he puts the resistor in place, and then measures the voltage drop across the resistor, and also across the choke (first choke, if I understood correctly). He then uses Ohm's law for the resistor, and for the know DCR of the choke, and comes up with the seemingly discrepant results for the current.
Many things could be going on involving the AC component across the choke causing complications, as has been suggested. Especially if it is the "first choke," which I would take to mean the one closest to the rectifiers. There will be a lot of AC across that choke. Who knows how the voltmeter, set to measure DC voltage, will respond when a small DC voltage has a large AC voltage superimposed? It could depend a lot on the specifics of the particular meter that is being used.
Of course another possibility could be a leaky smoothing capacitor. But on balance, I would expect the AC superimposed on DC complications in the measurement to be the more likely explanation.
Chris you got the whole picture. Did both channels close to same results so probality not a cap issue. I think the AC check with the scope is next up. The meter was a fluke 87 but I have others. Might try different dvm's just for the education.
A scope may not even tell the whole story. Unless you have a current probe you can only measure voltage.
I have done work on large megawatt class UPS systems where you must use a current probe to check SCR commutation waveforms. A voltage measurment won't wotrk.
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