a real challange?

[Penthode]

I viewed the YouTube video and you either have an IF alignment problem or a problem in the video amplifier (open peaking coil). The black streaking suggests the phase response is very bad.

Stagger tuned stages are optimised for both correct phase and frequency response. It is essential that the manufacturers alignment instruction be followed to the letter.

But I must ask, do you understand the concept of the split sound design and vestigial sideband demodulation? Because unless you do, you will continue to go around in circles.