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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Newbie bias voltmeter readings question posted by hartwerger on November 30, 2006 at 17:30:45:
you gotta find out if you're supposed to measure millivolts and TRANSLATE millivolts into milliamps, or whether you've been given true milliamp reading points.If you're measuring across a 1 ohm resistor, then one millivolt of voltage drop (difference, end to end) indicates or translates to one milliamp of current, because E=IR; if the current is 280 milliamps, then 280 millivolts (measured across 1 ohm resistor) times 1 ohm = 280 milliamps.
If you're reading across a 1 ohm resistor, then a millamp READING is meaningless; you're measuring a shunt current and you have no way of knowing what it represents.
Now, if the two measuring points are really giving you a current measuring link - and it's a little hard to know how that would be done unless there's a switch that puts your millammeter in series with the current, although a shunt arrangement could be set up - but in that case you're not actually measuring the current through the cathode, you're measuring a shunt current that corresponds to the cathode current in some predetermined ratio - all in all, not bloody likely - but if you are, then the millivolt reading is of no particular meaning.
My guess is that you are supposed to be measuring millivolts, and you're reading a voltage difference across a 1 ohm resistor, and thus whatever reading you get in millivolts is the same number as the cathode current in milliamps.
So, without knowing whether you're supposed to be measuring millivolts or milliamps in the first place, or without knowing the schematic, it's pretty close to impossible to figure your question out.
P.S.: I was also assuming you're measuring individual EL84 cathode current; if these are in push-pull pairs, and each pair shares a single cathode resistor, then the current you determine is actually double the current per tube.........
not enough data.
best, charles
"It ain't a comeback until it's left the shop" Jimmy Dunne, the first man to drive a VW Beetle faster than 200 mph, and he has the forehead scar to prove it; I will always honor him for taking a chance on me when I wanted to be an engine mechanic.
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- Re: Newbie bias voltmeter readings question - radiance 11:12:05 12/06/06 (0)
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