Mighty Monarch of The Air

[old_coot88]

Originally Posted by vts1134

I think the contrast control might be bad. When I rotate it in one direction it becomes shorted to ground. Adjusting the control does not give me similar contrast adjustment in the raster. If I adjust the control quickly the raster sort of flashes briefly and then goes back to the original level. I've previously cleaned the control with contact cleaner and the knob rotates freely.

If you put an ohmeter on the control, from the wiper to the 'top' end (which goes to pin 3 of the 12AU7) and rotate the control, the meter should reveal any rough spots or drop-outs. An analog meter is preferable as its needle will follow the control's rotation, while a digital meter just gives a bunch of hard to follow jumping digits.

Is it possible to temporarily use a normal 1500ohm resistor in it's place for testing purposes?

Actually the resistor will give you minimum gain (contrast), while shorting the 'top' end of the control directly to ground will give maximum gain.
oc