G7 Power Supply Transformers

I'm a bit lacking when it comes to design theory, but was wondering the purpose of the step up transformer in the power supply if you're getting 120V from the wall.  Could I avoid this transformer and just take outlet voltage to the rectifier (fuse inbetween of course) or would amperage be a problem?  I asked a proffesor to look at the power supply schematic, asking if I could use a couple transformers for a duel supply, and he told me I only needed one transformer total.  This was the Bio Med proffesor that once answered a student "It's a math thing", so I don't know if I should trust him...

Thanks for answering my more than likely stupid question,
Mike

No, no, no. Do not rectify the mains power directly under any circumstance!!!
You need the isolation of at least one transformer to stay alive!

You need the step down to get low voltage for the heater of the tube.
Then you need the step up to power the plate of the tube with high voltage.

If you find a transformer that can do both you can just use that.
www.tubesandmore.com has the P-T292 which works with a little adjustment
to the filter resistors of the power supply.

Haha, I figured it was a bad idea.  Could I use a single transformer for a double supply?  Thanks for the quick answer tk!