Subbing the yoke looks like quite a hassle. My very first thought on seeing the image
http://www.videokarma.org/attachment...4&d=1694521711 was a very large ripple(hum) on the main B+ line. Even if the main filter caps have been replaced, possibly a miswire(?) could be allowing a large ripple (since the vert sweep is locked to the powerline freq., a ripple would be stationary instead of a "crawling hourglass". Before doing a yoke swap, I would first want to verify that the main B+ is clean. Do you have a schematic for the unit?