Interesting Filament Circuit

[Tom9589]

Tom, You are exactly right. The plate voltage for the 1st video IF stage comes off of the cathode of the 2nd video IF stage. Therefore, the cathode of the 2nd stage is way above ground and would need the extra transformer.

Now that begs the question: Why did they make those two IF stages in this unusual configuration?

IIRC, the tube whose filament was driven by different voltage sources was the mixer tube in the tuner.

I had a Knightkit amplifier in the 1960s that had that exact configuration to provide DC to the filament of the first amplifier stage. Took forever to warm up.