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Originally Posted by Steve McVoy
Replacement flybacks were not exact replacements for the originals, and often circuit changes were required to get them to work, by trial and error. I'd try increasing the resistance of the screen grid resistor to see if the width goes down without significanly affecting the high voltage.
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Well, I've tried doing that and all the other 'fixes' I can think of.
I can make it 'better', but not right. Everything I tried sort of works, but causes a great reduction in the HV.
I really think now that the flyback is a 'close but no cigar' replacement for the original regardless of what the parts crossover iindex says.
I tried increasing the size of the screen resistor, even doubling it, and
got a little reduction in width, but lost HV, down to 8.3 KV. So I put the original value, 4700 ohms, back in and got the lost HV back, 10.7 KV.
I tried placing a spare width coil in series with the return lead of the H yoke winding and this helped reduce the width, and did not cause any noticeable linearity problem, like putting a resistor in series did. This alone did not reduce the width nearly enough, however. The circle in a test pattern still looks like a football.
I tried soldering several different size inductors across the set's width coil. A 20 microhenry inductor worked as far as reducing the width to normal, [along with the width coil placed in series with the yoke] but with an accompanying loss of HV, down to 7.9 KV, so this is not the answer either.
I guess this added inductor overloads the flyback so I took the width coil and the 20 uHy inductor back out.
In all these experiments, I tried varying the width and lin. coil settings, tried a smaller lin coil tuning cap [.047 down to .027] and tried various settings of the drive cap and the results were always that there was a significant loss of HV that accompanied the reduction in width.
I compared several different 50T Philco schematics and found several different
connection schemes for the flyback, so I tried them all and they made no noticable difference in the excess width and gave no increased ability to reduce it.
In all this work, I found two significant sources of information which are well worth the time to study and understand.
The first is the 'Damper Tube History' article on Steve McVoy's Early Television Foundation website. This piece gets down to the nitty gritty of the development of the Horizontal Deflection system like none other I have ever read.
The second is a Sams book, 'Servicing TV Sweep Systems' by Jesse Dines,
publication # SSD-1. Another source of hard to get information about how
things work. It even has a section on reducing width!
The only thing I have not tried is the 'Zenith' method of setting sweep width.
I also don't know if this will work with a magnetically focused CRT or not.
I will have to make a non-ferrous metal shim out of very thin sheet brass stock to wrap around the neck of the CRT and slide between it and the yoke.
Positioning it properly looks like a lot of work, with many trial and error tests.
This involves disassembling the CRT mount, the focus coil, the yoke, and finding a way to keep the shim in place if it works, and insulate it from the yoke coils, not to mention the difficulty of getting everything lined up each time I want to move the shim.
Woof!
Film @ Eleven.
Cliff