[old_tv_nut]

I'm surprised that the detector output is that large, 10 Vpp. I was guessing something more like 4-5 v p-p.

The injection amplifier has a gain of 4.7x, so will only have 4.7 v p-p out. You can increase the gain by making the 470 ohm emitter resistor smaller, but it will be hard to get a 10 v pp signal out with a 12 volt supply. Your pot will have to be adjusted carefully, and because of the AC coupling, the DC will drift up and down with scene content, clipping whites in a dark scene or sync in a bright scene. To keep things stable, you will need a DC restorer.