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Bias probes/Am I getting true readings
Bias probes/Am I getting true readings
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Old 3rd June 2012, 01:26 AM   #1
krisjay is offline krisjay  United States
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Default Bias probes/Am I getting true readings

Hi all, I went ahead and bought a couple of the bias probes(they sit in the tube socket, then the tube sits in the probe socket) to use on a tube amp I have, the question I have is, am I getting true readings using a probe or is it skewed a little one way or the other, thanks.
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Old 3rd June 2012, 02:51 AM   #2
HollowState is offline HollowState  United States
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Location: Taxland, New Jersey
Whether the bias probe uses a 1 ohm shunt resistor or inserts your multimeter into the tube's cathode, the result is the same from a technical point of view. Any resistance introduced into the cathode circuit will affect tube current by lowering it a tiny bit. (I don't think any of these "probes" connect to the tube's grid.)

However, these resistances are very small and for all practical purposes can be considered negligible. So the accuracy you get will depend on the accuracy of any socket resistor (if used) and/or your meter. But in the overall scheme of things, a couple of milliamps either way isn't that critical and is close enough for audio.
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