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In Reply to: RE: Installing a current meter.. posted by DAK on June 18, 2017 at 13:24:13
Any good Simpson can be wired just like you say.
I like to include a fuse for insurance.
I have a pair of Japanese ones, they are mini meters, also 200 ma. Since the cathode current should be less than that. It should be ok to just wire it inline or series?
About the fuse If i size it at the same current as the meter it should be what you would want to do?
Thanx for the tips.
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.
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?
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.
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