Malcolm Irving wrote: ↑Sat Oct 06, 2018 9:22 am
In theory, twisting helps to cancel both the magnetic field and the electric field from the heater wires.
According to EE/physics theory there is no way that the heater wiring can influence hiss, just hum and buzz. But once Mojo enters the equations - who knows!
If the heaters are DC there is no need for twisting or close paralleling, of course.
Yes, the induced field radiates in a spiral 90°to the core plane of the twisted pair. That is as astonishing as anything one could consider as magic.
What I discovered was less ultra-ranged emission futzing with the signal wires if the heaters are pressed into the outside corner; not idle hiss, but the stuff that sounds like ultraviolet background radiation. lol I even tried an alternating foil shield from tube to tube swapping sides after every node. Totally not worth it, but hey.. seemed reasonable until you waste the time.
I think Fowler made an amp or two with the heaters on the outside. Someone did and the conversations about that setup almost had us make channels for the heaters to travel through to isolate them from everything else. When it came down to it, the foil experiments said there wasn't much to be gained (err.. enough to be gained) for the trouble.
DC heaters are effective. They break one of my design rules about simplicity in that everything we add is another simple point of failure. If you search forums about DC heaters you see enough instances of trouble.. you start thinking about other ideas.. I do. I think about physical isolation. It's always something.
The other thing is that there are perfectly excellent examples of amps that generally do anything you can imagine that were assembled by lesser primates in total darkness with cold irons. haha