Interesting Filament Circuit

[Tom9589]

I had occasion to look at the Motorola 10VT24R schematic today. The power supply uses a transformerless voltage doubler for the B+. There are two filament transformers. One transformer was connected only to the damper tube- not uncommon at that time. The other transformer has two 6.3 volt windings. One winding went only to the 2nd video IF tube. The other winding went to all the remaining tubes.

My question is why the separate winding only for the 2nd video IF?