From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: "mal hamilton" <g3kevmal@talktalk.net>,
              rsgb_lf_group@blacksheep.org
Date: Tue, 05 Apr 2011 20:20:59 +0100
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Subject: Re: LF: Decca Jeep
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OK, thanks.

M
=

> Mike
> The info that I sent yesterday for transformer windings are those
> specified by Decca for that particular transformer on that core.
> mal/g3kev
> 
> 
> ----- Original Message -----
> From: "Mike Dennison" <mike.dennison@ntlworld.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Tuesday, April 05, 2011 7:03 PM
> Subject: Re: LF: Decca Jeep
> 
> 
> Many thanks to Andy, Warren and Mal for their helpful info. It
> certainly looks like I have a shorted turn.
> 
> I will start by trying to dismantle the existing pot core, but I am
> not optimistic.
> 
> Warren's inductance measurements are very useful as I presume I just
> need to replicate those figures with my new core.
> 
> I have a couple of 3C85 toroids which could usefully be pressed into
> action.
> 
> But if anyone has a spare transformer (or even a Decca chassis minus
> the amps) it would save me some work.
> 
> And I am still baffled by the missing 3.3n cap shown on the circuit
> but nowhere to be seen in practice.
> 
> Thanks again.
> 
> Mike
> ====
> 
> > 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)   =   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
> > = 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 and Sec 1
> > or 2 mm enamel > > > de G3KEV >
> >
> 
> 
> 
> 
>