Quote:
Originally Posted by Kamakiri
Just so I'm following correctly, a misadjustment in this would potentially cause cathode resistor heating......is it likely that the resistors that were weak to begin with? I'm assuming the heating would cause failure, if the set were operated long enough, and the heating is being caused by an overload.
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Arrrrgghh! No. I was talking about sweep shrinkage that could be caused by misadjustment. This would be the result of the problem and not the cause.
I was also typing without thinking and changed subject in mid-sentence.
My one sentence expanded and written as three sentences:
Misadjustments in the syncro-guide circuit (page 18 above) could cause the sweep shrinking that you mentioned in your next post.
Other causes for this shrinking might be an incorrect horiz drive setting (the trim-cap), or a cathode resistor heating or one of the low voltage electrolytics in the horiz sweep. In short, anything in the horizontal sweep and sync circuits that causes a tube to pull too much current or simply a gassy tube can cause sweep shrinkage.
(Reasoning: Normally when a picture blooms, as you described, one assumes that it is a weak 1B3 or an isolating resister in the HV circuit. However, you mentioned that the image seems to be cropping while shrinking. This latter clue may or may not indicate a sync issue, especially the timing and/or pulse width, in the circuit where the horiz sync pulse is feed back to the sync tube, or simply a syncro-guide misadjustment.)
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On your Hickok scope, make sure you either have the original probes, or the circuit diagrams of the original probes, so you can repair or make new ones, as they are a needed part of the scope. A set of correct probes is needed not only for use, but for the safety of your scope.
My suggestion for now is for you to go ahead and set the TV by eye. After you have repaired your scope, you recheck the sweep and set the peaks and then recheck the whole process. My guess if that you will find it works better after being scoped. These controls do interact and can sometimes confuse an experienced repairman.
For the record: During the era that these sets were in use, one would sometimes find the linearity coil slug or both the slug and brass screw missing!