Thanks, that does look like the tube base. The Phillips 3NP4 data sheet is at:
https://frank.pocnet.net/sheets/201/3/3NP4.pdf
In an effort to eliminate more variables, I tried injecting video and audio directly at the amplifiers, bypassing the tuner and IF stages. The results were good, so I wired in cables and made a little junction box where I can plug in A/V cables from a DVD player, etc.
The picture looks better than before, and the audio is outstanding:
More details in my article at:
https://antiqueradio.org/Emerson609P....htm#Injection
The screen geometry is approaching normal. The picture is still somewhat off-center horizontally, a condition I hope to cure by raising the optical box using its bottom "tilt" adjusters.
Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html