heaters in parallel?

[Wilder Amplification]

NO !!! The secondary winding is center tapped... and on the center tap is applied the dc bias. There is no "heaters wired as a voltage divider".

They form a voltage divider ACROSS the full winding...not to ground. Wire two power tube heaters in series across a 12.6VAC winding...you'll have 6.3VAC across both of them.

Although if you ground the CT of a 12.6VAC winding, you'll have 6.3VAC to ground, so you could ground the heaters at the point where they join together in series.

In regards to magnetic field density, current flowing through a conductor generates a magnetic field around said conductor. The less current flow through the conductor, the lower the magnetic field density

drawings where they

Marshall DSL50

http://www.drtube.com/schematics/mar...60-02-iss7.pdf

Look at fuse F1 - F3 in this schematic. This is just one example.