[AMPS] floating a filament transformer

[craxd]

Jason,
Those ferrite rods increase the inductance so a few number of turns can 
be used to create a choke to block the RF out of the heater supply. A 
toroid with similar properties can be used here to. The wire you seen is 
merely magnet wire with a varnish insulation. Some have used regular 
insulated wire also, it just has to be insulated so it don't short out. 
Most rods are about 5-6 inches long with about 4 inches of winding on 
them. The wires (about 14-10 gage) are wound bi-filar where one wire is 
laid beside the other around the coil. If I recall, these were published 
in the ARRL Handbook at one time with a how-to included. The ferrite is 
about a #43 material or an iron powder could be used which type is by 
color code. In either case, it will operate within 1-30 MHz. As long as 
there's enough inductive reactance to block the RF, and the wire is big 
enough for the heater current, you got it licked.

Will Matney


I have been reading with interest about the filament chokes for 3-500Z,
etc.  In the photos I've seen of projects the filament choke appears to be
bare wires around the ferrite rod.  Am I seeing this correctly?  How does
this not short out and thereby not provide current to heat the filaments?
Or is this wire typically coated with some kind of insulating material.


73 jason N1SU