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Re: [Amps] Amplifier power supply?

To: Tom W8JI <>
Subject: Re: [Amps] Amplifier power supply?
From: Ian White GM3SEK <>
Reply-to: Ian White <>
Date: Sat, 14 Jul 2007 15:37:16 +0100
List-post: <>
Hello Tom W8JI
>> Can't see why not. Being toroidal transformers, the
>> magnetic fields
>> should be entirely contained within each individual
>> transformer.
>While it won't hurt his application, you'd be amazed at the
>amount of flux leakage from those magical self-shielding
>For example a iron T-94-2 mix core has enough flux leakage
>that the inductance can change about 50% between turns
>spread evenly around the core and turns compacted into one
>small area.
>I know all the propaganda states the donut somehow magically
>has zero flux leakage, but the real fact is other than path
>length the magnetic field has no idea at all it is in a
>round core, a square core, an oval core, or a conventional
>interleaved E-I core. It can be better than some other core
>shapes of the same material (for example it is a whole lot
>better than a solenoid with open ends), but it isn't
>anywhere near perfect.

That is important for RF applications, but mains application are several 
orders of magnitude away in permeability, numbers of turns and 

OK, enough theory...  Having an identical pair of toroidal mains 
transformers under the bench (about 50VA size), I just hooked one 
primary up to 230V 50Hz, and then used the other transformer's primary 
as a 'search coil'. With the two toroids sitting one on top of the 
other, the induced EMF due to flux leakage was 2 MILLI-volts! (That was 
the highest leakage I could find in any orientation. Loading the 'hot' 
transformer to full output made no significant difference either.)

Looks like you're good to go, Andy.


73 from Ian GM3SEK
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