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What dictates max horizontal width and vertical height
I have two sets in particular, but I see this from time to time. On my Hallicrafters electrostatic 7 inch seems that I can’t get the picture to fill the screen when HV is maxed out to 4.6kV. I understand that the sweep sensitivity of the estat CRT reduces as HV increases, so in my case the picture will fill the screen at lower than desired HV. At max HV, adjusting my vertical size and horizontal with controls will get to a point where the maximum allowable width is achieved and turning them up any more will cause fold over and compressed at least one side of the image.
At one point on this television, I thought maybe the bias was off on the horizontal output and vertical output tubes, but it does seem like it reaches its limits on both sides. At that point, I thought maybe it needed to amplify more current so I made a goofy device that parallel the guts of two 12AU7 tubes with the heaters arranged to act like the 12sn7. The device worked just fine however, the output was not any better than previously with the original 12SN7. So at this point, I guess I’m lacking voltage swing?
Either way, has anybody encountered this problem and solved it? I’m having a very similar issue on my Emerson 637. Barely enough vertical height, and just shy of filling the screen horizontally with the same symptoms of horizontal and vertical cranked up the sides will compress and or fold over.
These sets are completely recapped, including electrolytic cans etc, all sweep tubes and rectifiers are either NOS or strong testing. I did replace the plate and cathode resistors for vert and horiz. in the Hallicrafters and it actually made it a bit worse, the plate resistors drifted up almost twice their value, and that seemed to squeeze a little more gain out of the horizontal output stage. But now everything has good resistors at their proper value and I still can’t get a full-size picture.
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11-28-2025, 10:27 AM
Linear Mode
