Predicta pedestal vertical hold

[judge]

Maybe I should have started a single thread on this restoration. Anyway I thought I would start a thread about an issue I am having with the vertical hold not being stable. It will lock on for a while then roll, then lock etc. etc. Perhaps not coincidentally, the horizontal hold is finicky. The picture will tear before it locks on, and then the picture may or may not snake.

This predicta basically 'worked' prior to me starting work on it. I have replaced all the electrolytics, paper caps, black beauties etc., plus all the resistors on the main board, the big resistors on the chassis, the diodes, and the thermistors. In particular, although it had several other issues, it did not have this one specific issue.

Anyway - fiddling with the tubes shows that the 10DE7 was loose. I tightened up the socket so it wasn't as loose, but it had no effect other than fiddling with it no longer caused the picture to collapse.

As a next step, I ordered replacement tubes, including the 10DE7. A few have arrived and been fitted (not that one yet) and it looked like that fixed the problem, but after a few more rounds of messing about with the tubes, the instability was back. I had to mess with the tubes some more because one of them was DOA, so it took a while to isolate which tube was bad. BTW it tested well, but just doesn't work when inserted - the 12DQ6A.

I will wait until I have tried a new 10DE7 before going any further, but scouring this forum and antiqueradios.com shows there are quote a few possible causes of this instability, so this may take a while. I'll update this thread with progress.