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References: <Pine.LNX.4.64.1601072157400.1618@plato.ucs.mun.ca>
	<15220ed436f-4a49-35d4@webprd-a06.mail.aol.com>
Date: Fri, 8 Jan 2016 18:50:02 +0000
Message-ID: <CAA8k23SGvY46yx8UpE72_gWJWbuEj1HMrQsg3AD6Yj9r0G=7BA@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Decca 5501
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The fact it is a GAPPED core is of more significance than that of the type
of ferrite.   In a transformer application - as that appears to do - it is
surprising that a gapped one is used.   I do not have the circuit of the
Decca transmitter to hand, but can only assume the driver has DC passing
through the winding, hence the need to introduce an air gap to prevent
ferrite saturation.

In which case, the fact your unit overheated suggests your gap was too
small and the Vt product (volt-seconds is what saturates ferrite, not
current).   BUT if that was the was the original unit, you need to ask the
question why it should have failed before trying to replace it.    Those
transmitter units were very reliable under rated things, so components
failing need investigating.

Andy  G4JNT

On 8 January 2016 at 11:09, <gw8glo@aol.co.uk> wrote:

>
>
>
> Does anybody know what ferrite grade is used on the fet driver
> transformer. I have had one burn out and have rebuilt it but would like to
> redesign it with better isolation between windings. Have tried various
> cores but cannot get the same clean waveform. The original is a gapped core
> of unknown material ferrite. Does anybody have a scrap amp unit that I can
> use for testing. The finished mods have given 1 kw at 53 volts, can be
> driven up to 75 volts but dummy load cannot take it!!!
> 73 Dave GW8GLO
>

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<div dir=3D"ltr">The fact it is a GAPPED core is of more significance than =
that of the type of ferrite. =C2=A0 In a transformer application - as that =
appears to do - it is surprising that a gapped one is used. =C2=A0 I do not=
 have the circuit of the Decca transmitter to hand, but can only assume the=
 driver has DC passing through the winding, hence the need to introduce an =
air gap to prevent ferrite saturation.<div><br></div><div>In which case, th=
e fact your unit overheated suggests your gap was too small and the Vt prod=
uct (volt-seconds is what saturates ferrite, not current). =C2=A0 BUT if th=
at was the was the original unit, you need to ask the question why it shoul=
d have failed before trying to replace it. =C2=A0 =C2=A0Those transmitter u=
nits were very reliable under rated things, so components failing need inve=
stigating.</div><div><br></div><div>Andy =C2=A0G4JNT</div><div class=3D"gma=
il_extra"><br><div class=3D"gmail_quote">On 8 January 2016 at 11:09,  <span=
 dir=3D"ltr">&lt;<a href=3D"mailto:gw8glo@aol.co.uk" target=3D"_blank">gw8g=
lo@aol.co.uk</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" sty=
le=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><font =
color=3D"black" size=3D"2" face=3D"arial">

<div> <br>

</div>


<div> <br>

</div>


<div> <br>

</div>


<div style=3D"font-family:arial,helvetica;font-size:10pt;color:black"><font=
 size=3D"2">Does anybody know what ferrite grade is used on the fet driver =
transformer. I have had one burn out and have rebuilt it but would like to =
redesign it with better isolation between windings. Have tried various core=
s but cannot get the same clean waveform. The original is a gapped core of =
unknown material ferrite. Does anybody have a scrap amp unit that I can use=
 for testing. The finished mods have given 1 kw at 53 volts, can be driven =
up to 75 volts but dummy load cannot take it!!!<br>
73 Dave GW8GLO<br>
</font>
</div>

</font></blockquote></div><br></div></div>

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