DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:date:message-id:subject:from:to
         :content-type:content-transfer-encoding;
        b=iWAu1anh9WPIqGRlpKekHxcgUSWxqeeQMBpnrR7A0G67q5mkBtKEf6uWCws0V/2aMT
         29sDwSgtH1ZlaU3jEop9WR3ACZEs/+n6wdGfCwz+C6LKdZYUFYf7VWGOC+bu16b7BlGn
         dExNlIc1dizFbZgdzyhVJgkZwviNKdMO4kBlU=
MIME-Version: 1.0
In-Reply-To: <4D9B676E.27668.4B358A@mike.dennison.ntlworld.com>
References: <007f01cbf2f6$2d7574a0$0401a8c0@xphd97xgq27nyf>
	<BANLkTin9nFF29qfkiLaFy+fszB2dGa=3eA@mail.gmail.com>
	<4D9B676E.27668.4B358A@mike.dennison.ntlworld.com>
Date: Tue, 5 Apr 2011 19:18:30 +0100
Message-ID: <BANLkTinuS+RQgjdeMa4J5qxJO5Qrf+TmRg@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: Re: LF: Decca Jeep
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Don't worry about trying to replicate inductance values or even worry
about it tahy don't matter, and probably vary all over the place with
temperature.  High u ferrites aren't reknowned for temp stability.  In
a transformer inductance is not important - provided it ends up  than
enough.

Use the equations I posted yesterday to get your number of turns based
on Bmax.  Keeping to < 0.1T or perhaps even lower.

Andy
www.g4jnt.com


On 5 April 2011 19:03, Mike Dennison <mike.dennison@ntlworld.com> wrote:
> 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
> =3D=3D=3D=3D
>
>> Any large modern SMPSU core will cope with 1kW of sinusoidal 137kHz
>>
>> Just make sure B is kept below =A0~0.1 Tesla using the equation to
>> determine teh minumum number of turns
>> =A0V(rms) =A0 =3D =A0 4.44.F.N.A.B
>>
>> F =A0Hz, =A0 N =A0turns =A0 A =A0core x-sectional area in m^2, =A0B Tes=
la.
>> =A0(the factor 4.44 comes from =A0SQRT(2) * PI )
>>
>> In my 137kHz 700 Watt Tx, =A0 I used an ETD49 core with cross sectional
>> area of 200mm^2 =A0made from 3C85 material designed for Bmax =3D 0.05T.
>> That runs cold. =A0 =A0Thes days, even better ferrites are availble, li=
ke
>> 3C90. =A0These 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. =A0Although 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. =A0 =A0Just don't use too many turns that copper loss=
es
>> 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 >
>>
>
>
>
>