[BeamT]

Troubleshooting 2 issues, jail bars, unable to produce one or more service lines in setup.

When you disconnected the IF input from the tuner, jail bars yes/no?
When you removed the IF module, jail bars yes/no?
When you inject the video source from your generator at C1, IF Module out, jail bars yes/no?

The 6.99v shown at C1 in SAMS is a DC value, to the right 1.4v P2P is the waveform involved and is roughly what your generator is supplying. Not every set has a IF Module that can be removed.

The 24v DC supply is very important, 121-808 looks like a good sub for 121-966. Higher values and a different case, but looks good. You noted in prior threads the voltage at the test point was good. Did you replace this transistor before?

What is the "ground loop" you are referring to?

The strategy behind measuring the DC values on the CRT is to rule out a circuit issue and unfortunately implicate the CRT. You appear to have good gray scale with what you have, good focus, convergence is really good.

I've never worked on an Avanti, which I believe your set is, do these NOT have a Service Saver plate on the bottom?

Might be interesting to test your setup switch with your ohmeter before you go to the trouble of replacing it.