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Originally Posted by Einar72
Not knowing whether the old flyback fried itself, or any other components, I have one important question: Did you check each resistor in the circuit for changes in value? I'm curious about the cathode resistor of the H. output tube, I assume you are measuring the cathode current with a meter in series? Is there a drive or coupling adjustment between the oscillator and the output-tube grid? Are there alternate taps for the yoke on the FLY-1? Lastly, what is the output tube? Hopefully, this info will help some others to take a stab at this.
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The original yoke H windings shorted to ground, causing the flyback to short.
The replacement yoke is another original Philco of the same number from a similar 12 inch Philco set. I checked all the resistors. The cathode of the 6BG6 is grounded and develops -19 volts contact bias on the control grid.
Measured stage current at 129 mA by pulling the 1/2 amp Damper fuse and connecting ammeter across the fuse holder, as per Philco instructions. The Drive control has minimal effect on the width. Followed Philco instructions in setting it to eliminate drive line in picture.
There are no other output taps on the FLY-1, and the 10.8 KV is about 20% higher than the 9.0 KV Philco specification. This seems to correspond with the amount of increased width.
The 6BG6 screen has 290 volts, as per specs, through a 4700 ohm resistor from B+.
Would I endanger any critical components if I increased the size of the 6BG6 screen resistor to lower the screen voltage? Might doing this reduce both the width and the high voltage?
As stated previously, I have not tried any 'fixes' yet.
Thanks for all the comments and suggestions.