OK, this shows a DC restorer before the sync separator, So you should not need one in your input circuit, at least not for sync.

I suggest the following to try to chase one problem at a time:

1) Adjust the gain of the transistor amplifier to get normal contrast.
2) Leave it there.
3) Chase the hum bars.

To make sure I'm following right, does the cathode of VT6a (pin 3) go to pin #6 of plug P7 and hence to R201?

OOPS - I see the DC restorer is not feeding the sync separator. But since it is AC coupled to start with, you do not need one in your circuit for that purpose.

Got my wires crossed and I now see the DC restorer is for the video - this also means you don't need one in your amplifier circuit.

By the way, where are you getting the 12 V supply for the amplifier? Any hum, noise or instability of the supply will transfer directly to the output on the collector.

What do you mean by this?


Yes

This is a good point. I can try various power supplies to see if the problem goes away/changes with another supply. I'll take a few home tonight and experiment.

Why not use a battery? 9V would probably run it OK, and drain would be minimal. Give it an on/off switch.

(Hum bars are the horizontal dark shadings in the raster due to 60 or 120 Hz ripple (hum).

I actually have a 12V battery in my pocket for that purpose. I figured I'd start there with my power supplies as it would be the "cleanest" supply.

As oldcoot88 said, hum bars are those dark horizontal bars that run upward or downward in your video. I now notice that they seem to change direction during the time recognizable video is on the screen. This should not happen if the video vertical rate is stable and the hum bars come from the power supply (AC line). What is your video source? Could it be accelerating up to speed? It just seems weird.

You also have white retrace lines, which have to do with CRT vertical retrace blanking (or lack thereof) and maybe copy protection on the video source.

So, again, the thing to do is to set the video level correctly to get a stable picture, and then chase the interference issues.

Good idea.

It was the power supply. Using a 12v battery eliminated the vertical bars. I have two other video problems that will need to be addressed, but I need to ascertain whether the problems come from the inverter, or are inherent to the set. I'll report back after some experimentation.

I've had precious little time to spend at my bench, but I did manage to sneak this 10 second video in on where I am. There is some crazy interference happening right now that I wanted to show you guys. I hope some one has seen this before and can point me in a direction. I am using shielded video cable (I thought that might be the issue). Any one ever seen something like this? https://youtu.be/zgcznUOokvw

P.S. I will try to get some time today to fire up the B&K 1077 and see if the issue persists when using it to inject video instead of the video circuit we made.

I'm continuing this topic in a thread about the restoration of the television in which I will be using this amplifier. Here's a link to that thread http://videokarma.org/showthread.php?t=268361