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Date: Mon, 4 Apr 2011 20:44:58 +0100
Message-ID: <BANLkTin9nFF29qfkiLaFy+fszB2dGa=3eA@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Decca Jeep
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Any large modern SMPSU core will cope with 1kW of sinusoidal 137kHz

Just make sure B is kept below  ~0.1 Tesla using the equation to
determine teh minumum number of turns
 V(rms)   =3D   4.44.F.N.A.B

F  Hz,   N  turns   A  core x-sectional area in m^2,  B Tesla.
 (the factor 4.44 comes from  SQRT(2) * PI )

In my 137kHz 700 Watt Tx,   I used an ETD49 core with cross sectional
area of 200mm^2  made from 3C85 material designed for Bmax =3D 0.05T.
That runs cold.    Thes days, even better ferrites are availble, like
3C90.  These are less lossy still, but Bmax is no more.
TV LOPTs use generally older types of ferrite, even older than 3C8, so
its worth going for a modern SMPSU core rather than cutting corners
dismantling old TVs.  Although as Mal has clearly found, using LOPTs
beyond their design frequency, provided B is kept low by using enough
turns, even they will run OK.    Just don't use too many turns that
copper losses begin to rear their head.

Andy
www.g4jnt.com


On 4 April 2011 19:29, mal hamilton <g3kevmal@talktalk.net> wrote:
> Output transformer info.
> Faulty output transformer.
> Strip old transformer windings and rewind as follows.
> Prim 3 x 6 turns Sec 31 turns
> or
> use large LOPT 3C material with same amount of turns as above.
>
> Wire guage guide Prim 3mm litz per winding=A0and Sec 1 or 2 mm enamel
>
>
> de G3KEV
>