This scope photo shows the AC line voltage, ferroresonant transformer capacitor voltage, and -15V transformer tap voltage. The AC voltage was varied from 105 to 120 volts with almost no change in the output voltage.
| AC Voltage | 10V Output | -15V Output |
|---|---|---|
| 100 | 10.83 | 15.11 |
| 105 | 10.78 | 15.06 |
| 110 | 10.74 | 15.02 |
| 115 | 10.72 | 15.00 |
| 120 | 10.68 | 14.96 |
The somewhat sinusoidal waveform is the AC line at 50 volts per division. The taller flat topped is the 15V transformer output at 5V per division. The shorter flat topped is one of the transformer capacitor terminals at 100V per division. The ferroresonant transformer outputs are much closer to a square wave than the normal transformer sinusoidal outputs. Looks like my AC line has pretty high harmonic distortion. Rectified capacitor loads tend to flatten the tops of the sine wave.
For this one I used my Tektronix 547 oscilloscope which is a nice oscilloscope of similar age to this computer. I did use a digital camera for the photo instead of the period Polaroid. I took two photos with the different line voltage and overlayed them. The previous traces are either directly from my new digital scope or data captured with it and processed with Octave. The previous cartoon is from Jim Williams who used a Tek 547 for his work until his recent death.
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