Re: AVO CT 160 Improved Anode Current Measurement
David,
basically you are right of course. Accurate measurements do require a reasonably stable AC mains. Fortunately this is less an issue where I live. Attached is what I have measured last night when the world around me was asleep and AC was stable then. The single line red and blue curves are the measured Ia=f(Ug). The thin black lines inside the two curves are their 2nd order approximation polynomials. The straight double line red and blue curves are their respective differential functions (calculated gm)=f(Ug). The closeness between measured and calculated gm values provides an assessment of the measurement accuracy. Not too bad for a 60+ year old instrument.
I have also tried to assess the sensitivity of the anode current backing off equilibrium against small power variations. As a test I switched on my hot air gun plugged into an outlet next to the CT160. Its meter needle danced nicely +- ca. 10 millivolts with the on-off rhythm of the air gun thermostat. Next I will borrow the magnetic power stabilizer from our son's hifi and try it as a remedy. Doing that I hope that the stabilizer will not create another problem by distorting the AC sinus to the CT160.
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