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In Reply to: RE:I have a 200ma Fluke or something like that. posted by DAK on June 18, 2017 at 16:55:51
Using a ma meter as a ma meter should be straight forward, but not all ma meters are created equal, some expect you to know to put in a shunt resistor but others have this built in. Use a battery and a resistor, figure out current and put the meter in series, if it reads correctly (you can verify with a digital meter), then fine, just insert it. That being said, I'm always nervous of wires and screw terminals coming lose so I put a shunt to ground, like 100 ohms. The small resistance of the ma meter will swamp that resistor in normal practice, but if the meter connection opens, the output tubes will not red-plate.
Follow Ups:
Ok, if i understand you i will have the meter to ground and from the same poiint i would also install a 100 ohm resistor to ground to act as a fail safe in case the meter fails?
Yes
If standard cathode bias, an open cathode shouldn't red plate the tube?
I think the OP mentioned going from cathode to ground, though I could be wrong, and that implied fixed bias to me but yes, if it is cathode biased, not an issue.
Yes
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