[old_tv_nut]

Originally Posted by old_coot88

If I had stumbled fresh onto seeing the screen shot in post# 60, the first thought woulda been "borderline-weak H output tube". And the first move would have been the "7 seconds off" test. That is, with the set running, turn it off for about 7 seconds, and back on. If the width is slow to fill back out, the tube may be borderline ('specially if it's been red-plating much). Whereas if the width comes back quick, the tube is obviously good.

It's a 'quick & dirty' little test that can also show up other borderline tubes. E.g., H oscillator, color oscillator, vert output, RF amp.

Yes, this could be it.

A circular test pattern like the Indianhead would show the bad horizontal linearity in this case (compression on the extreme right), but you might also be able to detect it with a crosshatch.