From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 05 Apr 2011 19:03:10 +0100
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Subject: Re: LF: Decca Jeep
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Many thanks to Andy, Warren and Mal for their helpful info. It=20
certainly looks like I have a shorted turn.=20

I will start by trying to dismantle the existing pot core, but I am=20
not optimistic.

Warren's inductance measurements are very useful as I presume I just=20
need to replicate those figures with my new core.

I have a couple of 3C85 toroids which could usefully be pressed into=20
action.

But if anyone has a spare transformer (or even a Decca chassis minus=20
the amps) it would save me some work.=20

And I am still baffled by the missing 3.3n cap shown on the circuit=20
but nowhere to be seen in practice.

Thanks again.

Mike
=3D=3D=3D=3D

> Any large modern SMPSU core will cope with 1kW of sinusoidal 137kHz
>=20
> 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
>=20
> F  Hz,   N  turns   A  core x-sectional area in m^2,  B Tesla.
>  (the factor 4.44 comes from  SQRT(2) * PI )
>=20
> 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.
>=20
> Andy
> www.g4jnt.com
>=20
>=20
> 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 >
>=20