Poor focus on an Admiral 20Y1

[Eric H]

I had a focus problem on a Admiral a while back, I don't remember what fixed it, but I seem to recall a bad coil. Have you ohmed the coil out? Also I seem to remember the polarity of the coil is important, not likely it got reversed but possible.

Is the best focus at one end of the control or does it pass through the best focus somewhere in the middle without actually focusing?
If it's at one end it would indicate it's either not getting enough current or getting too much.

Have you tried another CRT?