Electric OU: Quantitative Scoposcopy and Tar Baby Bias Current
Here I show the calibrated Hickok meter in series with TarBaby’s negative bias supply using the potentiometer and a regulated power supply (the PS instead of a 9v battery, for stability during the demonstration.) Then I demonstrate the relationship between oscillation onset and amplitude, and the negative bias current as indicated on the calibrated Hickok moving coil laboratory milliammeter. Finally, I use the HP180a precision analog oscilloscope to view the voltage drop across the 10.3 Ohm series resistor at the potentiometer’s slider. Using the scope’s vertical amplifier setting of one volt per division and the 10.3 Ohm resistance and the Ohm’s Law relation I=V/R, the “eyeball” determination of the current agrees closely with the reading from the calibrated laboratory moving coil meter.