[Username1]

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"Do you agree that the caps across the video output collectors should have killed the
banding if it was wholly present in the video?" - No, because a cap in that spot, or
any spot will only partly reduce, or enhance any interference. You could only
completely remove it if you set a bias in the signal drivers, and removed
any possible signal from effecting the drivers, tube or transistor. Not
to ground the base, but bias it and cut the input signal So you don't
drive it into saturation, or cutoff.

I'm pretty sure the interference is from the Horiz circuit as the lines are stable
with respect to the horiz sweep. Is it magnetic? Not sure, that is why I thought
moving around a piece of steel might show something. Most likely it's
electronic, a harmonic that is not sufficiently terminated in this design,
or it is and a component is bad, a circuit trace is broken, ground broken,
something just allowing a harmonic large enough that you see it
on the screen.... Bad coil, cap, etc, around the horiz drive,
flyback, yoke, you name it, it's in that area, or something
is picking it up & sending it through the set.

The problem with the interference in the power supply is that it will be present
in all amplification circuits - even if they are biased on in steady state and
not doing anything else.... Think about a bad filter cap in an old 5 tube
radio, I'm pretty sure we have all heard it. Volume effects it a little,
if it has a tone control it will effect it a little, and being on a station
will effect it a little too. - But is it in the signal path?

I once had a white hum bar floating through a tv picture, Naturally I thought
it was a cap, so did everyone else... The set went around the shop till I got it
back and changed some tubes.... Turns out it was a heater cathode short
in one of the video tubes...


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