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-   -   7” electrostatic set deflection shortcomings (http://www.videokarma.org/showthread.php?t=277809)

CJVx 09-09-2026 06:37 AM

7” electrostatic set deflection shortcomings
 
Has anyone else experienced short vertical height, only to fold over and crowd past a certain level, and not enough horizontal width, again with crowding past a certain level? Currently working on a Halicrafters and a Tele-Tone. And they both exhibit the same symptoms. The only 7 inch set that seemed to have enough to fill the screen was a Motorola VT71 that I worked on.

Anyway, I have gone through both sets, caps replaced, verified and replaced some tubes, verified filament voltage is correct in the stings etc. Checked all and replaced most resistors in the vertical and horizontal circuits with some improvement, but still not able to stretch the picture fully across the screen. If I lower the HV, this will enable me to accomplish that but now I’m only down to about 3kv and picture quality suffers.

On a variac, the picture doesn’t actually start to shrink until I lower the voltage below 90, and I don’t get any extra picture expansion if I temporarily crank it to 130 V. I do gain some brightness though.

Yamamaya42 09-09-2026 09:09 AM

Bandersen has many videos on u-tube about e-sets, I have little exp in the subject, having yet to finish the T-TONE 149 I got this year, working mostly on tape decks.

The vertical section will always be more fussy when it comes to parts out of tolerance, so it's always good to check it end to end with a very discerning eye, and if any doubt, put in new known good parts, and especially if 2 resistors of same value are linked, like are on the control plates, sample a few, like 10 and pick the closest match, it will help with linearity.
And do watch his videos, they are very helpful.
bandersentv - YouTube

mrjukebox160 09-09-2026 10:04 AM

What did you replace the hi voltage caps with? Disc caps will cause this problem.

CJVx 09-09-2026 12:30 PM

Quote:

Originally Posted by mrjukebox160 (Post 3268105)
What did you replace the hi voltage caps with? Disc caps will cause this problem.

Hi, I used Wima 6kV film caps on both sets

mrjukebox160 09-09-2026 03:09 PM

I never tried those. I tried Russen disk caps and they didn't work correctly. These worked but are not cheap: https://www.justradios.com/ASCcapacitors.html

bandersen 09-09-2026 03:40 PM

Wima caps should be fine. I've used them in several sets.
Did you replace all the resistors in the HV bleeder network down to the vertical deflection plates?


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