Question about this schematic

[Dealbreaker]

Hello All-
New guy here.  No formal school or electronics training.  Just enough knowledge to be dangerous. I have been looking for a beginner project and a couple years ago, I happened upon the schematic below.  Since then, I have become more familiar with the various Fender circuits, and feel a little more comfortable with what's happening.  This leads me back to this amp.  I highlighted some places that are unusual (to me).  The first is the elevated heater voltage.  The designer/author says it minimizes 60 Hz hum.  Can someone comment on this?  I'm not getting it.  60 Hz is 60 Hz...How does elevating the heater voltage above ground keep it from creeping into the audio side of things?
The other thing is the NFB.  The author describes it, but the way the schematic is drawn, its either missing, or again, I am out of my lane and just don't get it.
I appreciate the help, and enjoy the board.  Thanks in advance for any nuggets you can pass along.

[Dealbreaker]

One other thing....If a PT could be sourced to supply heater voltage as another secondary, could the elevated heater trick be used safely?  Or is it necessary to utilize the second XFMR? 
Hopefully this attachment is easier to read.

[sluckey]

NFB loop... plate thru R14 and C2 to grid.

You don't need a separate PT in order to elevate heaters. A separate PT is used to supply 12.6VAC because it is probably very hard to find a single PT with HV secondary and 12.6 secondary.

[kagliostro]

At the moment I'm astonished by the NFB

Joined that way don't we have HV on the speaker ?

Franco

[sluckey]

At the moment I'm astonished by the NFB

Joined that way don't we have HV on the speaker ?

Franco

That red line is not part of the schematic. Someone who doesn't understand NFB drew that red line.

[Dealbreaker]

That red line is not part of the schematic. Someone who doesn't understand NFB drew that red line.

Yes, that would be me.  I hi-lighted (in red) the portions of the schematic that had me confused. 
Thank you for the help.  Is there a good reason to elevate the heater voltage here?  I still don't understand how that would work.
I'll look closer at the NFB and try to get my head around that. 

[sluckey]

Is there a good reason to elevate the heater voltage here?  I still don't understand how that would work.

Read this, especially the section titled "Heater Elevation".

     https://www.valvewizard.co.uk/heater.html

I'll look closer at the NFB and try to get my head around that.

The NFB loop... goes from the plates thru R14 and C2 back to the grids. Don't get any simpler than that!

[Dealbreaker]

Yes sir, I'm with you now. Audio out of pin 8 of V2 goes to the OT and also to R14, mixes with audio from pin 1 V1, and passes thru C2 to the input grids of V2.  I get it. I am used to seeing the path of NFB originating at the speaker output of the OT.  Obviously, more than one way to skin a cat. 
I'll take a look at the article you linked.
Thanks as always for the help.