[Elecraft] KPA500

[Ian White GM3SEK]

>From: "Vic K2VCO" <vic at rakefet.com>
>Obviously I haven't tried it (!) but I suspect that the
>external magnetic field from a
>toroidal transformer is much less extensive than that of the
>usual laminated type.

Tom W8JI wrote:
>Don't bet on it.   :-)
>

Tom and I discussed this on the AMPS reflector, back in 2007.  Flux 
leakage from a toroidal winding at 50/60Hz is MUCH less of a concern 
than it is with toroids at RF.

The specific question on AMPS was whether two toroidal transformers can 
be stacked closely together without magnetic interaction, and the answer 
was: Yes, they can. With two identical toroidal transformers sitting one 
on top of the other, I connected 230V AC to the primary of one and 
measured only a few millivolts on the open-circuit primary of the other.

That isn't quite the same topic as the flux leakage from a single large 
transformer, but it's a good indication that leakage can be very low 
indeed.

Obviously the answer will also depend on the quality of design and 
construction, not only in the transformer but also in the rest of the 
amplifier, because flux leakage is also affected by the external 
connecting wires. For the lowest possible flux leakage, it is important 
to minimize the physical size of the 'coupling loops' created by the 
connecting wires, especially if the stray magnetic fields can also 
interact with a steel chassis.



-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek