Predicta 17" HV question

[Phil Nelson]

I replaced the most recent scope pic with one that's easier to read. Refresh this page in your browser to make sure it shows up. The vertical volts/cm control is set to 5 volts/cm and the horizontal sweep time/cm control is set to 2 ms. The probe is at 1x.

I got out my HP 428B milliammeter to measure the current on the cathode (pin 9). Looks like about 38-39 ma. (The meter's set to 100 ma scale and the needle points to about .38-.39.)



I also tried measuring the old fashioned way by bridging a .1 mfd cap on the cathode connection and putting my probes across the cap leads. With my old Triplett analog meter, the reading looked like 36-38 ma, in the same ballpark.

If I interpret any of this correctly, it seems that cranking the Height control all the way up sends both the grid voltage and the cathode current too high, yet I'm still not getting full vertical deflection.

While doing all this, a couple of times I heard a distinct snap from the yoke area. Maybe it's time to remove the yoke and look at that thermistor.

Phil Nelson