From: G0MRF@aol.com
Message-ID: <c2d.2454a520.34902a76@aol.com>
Date: Tue, 11 Dec 2007 13:01:26 EST
To: ken.h.wright@btinternet.com, rsgb_lf_group@blacksheep.org
MIME-Version: 1.0
Subject: Re: LF: IRF530N in 500kHz PA
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=20
Dear Ken.
=20
I can only guess that the "never in the same positiion twice" is an =20
indication that you have oscillation and not amplification.
I have used the L C L network with success on bipolar transistors but with =20
mixed results with FETs.   You will get some very high voltages from  the=20
inductor connected to the drain, especially if the design Q is too  high.  P=
ossibly=20
this is killing the FET.
Can I suggest that a 1:4 broadband bifilar transformer would be a lot more =20
successful.   I have built many of these for driving larger amplifiers  and=20
also for driving the grids or cathodes of valve amps.  They seem quite  reli=
able=20
but would need a LPF after the transformer.
=20
Regards
=20
David  G0MRF
=20
=20
=20
In a message dated 11/12/2007 10:57:58 GMT Standard Time, =20
ken.h.wright@btinternet.com writes:

Has anyone experienced problems  using an IRF530N in a 500kHz PA?. I am usin=
g=20
an IRF530N into an L =E2=80=93 C =E2=80=93 L  output network the design para=
meters for the=20
network are input:10 ohms,  output 50 ohms, centre frequency 502.5 kHz, Q=20=
=3D 12,=20
giving, L1  38=C2=B5H, C1  3.7nF, L2  84=C2=B5H, C1 consists of a 3.3nF fixe=
d capacitor=20
plus a 2 gang  500pF variable, 3mH inductor in the drain. I have tried=20
driving the MOSFET  with a 5v positive peak signal, and with a 3v rms signal=
 sitting=20
on a +ve  bias, I have managed to obtain 5w into a Marconi TF1152A/1 (50=CE=
=A9)=20
power meter  about three times, but when 12v is removed from the PA and=20
reconnected there  is no output, C1 is adjusted for maximum power output, bu=
t is never=20
the same  position twice, and there seems to be a very critical adjustment o=
f=20
the drive  to obtain, a) an output, b) anything that looks like a sine wave,=
=20
although  when I have got it right there is a very good sine wave. Any ideas=
=20
anyone as  to what may be going wrong? =20






  =20

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<DIV>
<DIV>Dear Ken.</DIV>
<DIV>&nbsp;</DIV>
<DIV>I can only guess that the "never in the same positiion twice" is an=20
indication that you have oscillation and not amplification.</DIV>
<DIV>I have used the L C L network with success on bipolar transistors but w=
ith=20
mixed results with FETs.&nbsp;&nbsp; You will get some very high voltages fr=
om=20
the inductor connected to the drain, especially if the design Q is too=20
high.&nbsp; Possibly this is killing the FET.</DIV>
<DIV>Can I suggest that a 1:4 broadband bifilar transformer would be a lot m=
ore=20
successful.&nbsp;&nbsp; I have built many of these for driving larger amplif=
iers=20
and also for driving the grids or cathodes of valve amps.&nbsp; They seem qu=
ite=20
reliable but would need a LPF after the transformer.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Regards</DIV>
<DIV>&nbsp;</DIV>
<DIV>David&nbsp; G0MRF</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>In a message dated 11/12/2007 10:57:58 GMT Standard Time,=20
ken.h.wright@btinternet.com writes:</DIV>
<BLOCKQUOTE style=3D"PADDING-LEFT: 0px; MARGIN-LEFT: 0px"><FONT     style=
=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=3D2>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN lang=3DEN-GB     st=
yle=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Has anyone experienced problems=20
  using an IRF530N in a 500kHz PA?. I am using an IRF530N into an L =E2=80=
=93 C =E2=80=93 L=20
  &nbsp;output network the design parameters for the network are input:10 oh=
ms,=20
  output 50 ohms, centre frequency 502.5 kHz, Q =3D 12, giving, L1 &nbsp;38=
=C2=B5H, C1=20
  3.7nF, L2 &nbsp;84=C2=B5H, C1 consists of a 3.3nF fixed capacitor plus a 2=
 gang=20
  500pF variable, 3mH inductor in the drain. I have tried driving the MOSFET=
=20
  with a 5v positive peak signal, and with a 3v rms signal sitting on a +ve=20
  bias, I have managed to obtain 5w into a Marconi TF1152A/1 (50=CE=A9) powe=
r meter=20
  about three times, but when 12v is removed from the PA and reconnected the=
re=20
  is no output, C1 is adjusted for maximum power output, but is never the sa=
me=20
  position twice, and there seems to be a very critical adjustment of the dr=
ive=20
  to obtain, a) an output, b) anything that looks like a sine wave, although=
=20
  when I have got it right there is a very good sine wave. Any ideas anyone=20=
as=20
  to what may be going wrong?=20
<o:p></o:p></SPAN></FONT></P></FONT></BLOCKQUOTE></DIV>
<DIV></DIV>
<DIV>&nbsp;</DIV></FONT>   </BODY></HTML>

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