[Amps] filament choke

[Angel Vilaseca]

Hi,

On almost every grounded-grid triode amp design I have seen, the 
filament choke is an abt 35 uH coil wound on a 1/2 inch dia, 7-inch long 
ferrite rod.

Such a large unit is a bit cumbersome.
Instead of a rod, could the filament choke be wound on a ferrite toroid? 
It would have less flux leakage, be more compact. 

How large should the toroid be?

Since it is wound bifilar, the DC magnetic fields of the two windings 
would cancel. So could I use a  say one-inch dia. toroid for a 3 A 
filament current (for a GS 35 B)?

Vy 73 de HB9SLV Angel Vilaseca