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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Sun, 7 Jan 2018 17:34:09 +0000
Message-ID: <CAA8k23TgQWG5ocKDjHV3AA5ZnhX8mWhMwGGwkL6-PGc7CuLqsg@mail.gmail.com>
To: LineOne <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Progress? with the PA
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What core ?
What  dimensions ?

Does it obey the fundamental equation for saturation in a core ?
Vrms = 4.44 .F . N . A . B

F Hz,   N turns,  A core area area in m^2   B Tesla

Keep B < 0.1 and  ferrite saturation should be fine

And if it is saturating, you need more turns, not less

Andy  G4JNT


On 7 January 2018 at 17:26, N1BUG <paul@n1bug.com> wrote:

> http://n1bug.com/n1debug/ASB_LF_Amp-20171223.jpg
>
> Recall that last week I had increased turns on the output transformer from
> 3x5 to 3x10. That reduced heating of the FET but did not help to stabilize
> the PA. It would put 12 to 14W into the antenna before oscillation started.
>
> Today I changed it to 4x10 turns so it is now a 16:1 transformer. This has
> made a big change! The PA will now put more than 30 watts into the antenna
> before oscillation starts with 13V on it. For the first time I noticed some
> slight warming of the transformer. I think it is the core heating up, not
> the wire.
>
> If I put 19V on it, I briefly see almost 50 watts into the antenna but the
> transformer becomes hot very quickly and within just 3 or 4 seconds, power
> begins to drop rapidly.
>
> At this point I guess either:
>
> The core is not suitable material or not big enough...
>
> or
>
> Maybe it needs fewer turns (but this may lead to too much heat in the FET
> again?) At 30W output with 13V, that FET is already running quite warm with
> 4x10 turns.
>
> At least I finally found something that makes a change!
>
> 73,
> Paul N1BUG
>
>

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<div dir=3D"ltr">What core ?<div>What=C2=A0 dimensions ?</div><div><br></di=
v><div>Does it obey the fundamental equation for saturation in a core ?</di=
v><div>Vrms =3D 4.44 .F . N . A . B</div><div><br></div><div>F Hz,=C2=A0 =
=C2=A0N turns,=C2=A0 A core area area in m^2=C2=A0 =C2=A0B Tesla</div><div>=
<br></div><div>Keep B &lt; 0.1 and=C2=A0 ferrite saturation should be fine<=
/div><div><br></div><div>And if it is saturating, you need more turns, not =
less</div><div><br></div><div>Andy=C2=A0 G4JNT</div><div><br></div><div><br=
></div></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On 7=
 January 2018 at 17:26, N1BUG <span dir=3D"ltr">&lt;<a href=3D"mailto:paul@=
n1bug.com" target=3D"_blank">paul@n1bug.com</a>&gt;</span> wrote:<br><block=
quote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc=
 solid;padding-left:1ex"><a href=3D"http://n1bug.com/n1debug/ASB_LF_Amp-201=
71223.jpg" rel=3D"noreferrer" target=3D"_blank">http://n1bug.com/n1debug/AS=
B_L<wbr>F_Amp-20171223.jpg</a><br>
<br>
Recall that last week I had increased turns on the output transformer from =
3x5 to 3x10. That reduced heating of the FET but did not help to stabilize =
the PA. It would put 12 to 14W into the antenna before oscillation started.=
<br>
<br>
Today I changed it to 4x10 turns so it is now a 16:1 transformer. This has =
made a big change! The PA will now put more than 30 watts into the antenna =
before oscillation starts with 13V on it. For the first time I noticed some=
 slight warming of the transformer. I think it is the core heating up, not =
the wire.<br>
<br>
If I put 19V on it, I briefly see almost 50 watts into the antenna but the =
transformer becomes hot very quickly and within just 3 or 4 seconds, power =
begins to drop rapidly.<br>
<br>
At this point I guess either:<br>
<br>
The core is not suitable material or not big enough...<br>
<br>
or<br>
<br>
Maybe it needs fewer turns (but this may lead to too much heat in the FET a=
gain?) At 30W output with 13V, that FET is already running quite warm with =
4x10 turns.<br>
<br>
At least I finally found something that makes a change!<br>
<br>
73,<br>
Paul N1BUG<br>
<br>
</blockquote></div><br></div>

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