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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTin3w2PmwROGFzODvFcUO5-AL0vUyq8C7INdUYAe@mail.gmail.com>, <28093526.109907.1273582377168.JavaMail.fmail@mwmweb078>, <AANLkTil1Sx9v3lHUNUuJLm6EWcbmy0rsMMPHgyf58I3w@mail.gmail.com> <4BE97E93.12009.23FC007@dave.davesergeant.com> <4BE9ABA8.5000801@iup.uni-heidelberg.de> <4BEAA568.2060507@iup.uni-heidelberg.de>
Date: Wed, 12 May 2010 14:42:49 +0100
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Subject: LF: Re: 12V/300W VLF PA circuit
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Hi Stefan. I am not sure what the ICL7667 is but if it is a FET driver=
 chip
similar to the Texas TC4426 the outputs go high when the drive is remo=
ved.
See the 136 PAs by G3YXM and G0MRF for keying ideas.....they key the=
 supply
to the chip which is safer.
This effect accounts one of the few FETs lost to Class-E LF PAs we
experimented with.
Alan G3NYK

----- Original Message -----=20
From: "Stefan Sch=E4fer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, May 12, 2010 1:56 PM
Subject: VLF: 12V/300W VLF PA circuit


> Dear VLF,
>
> At http://www.iup.uni-heidelberg.de/schaefer_vlf/12V_300W_VLF_PA.pdf
> you can get the circuit of my 300W PA i used at all the VLF experime=
nts.
> The circuit is made in my well known simple hand drawing ;-)
>
> Many stns (at least 10) have recorded my 8,97 kHz signal so you know
> that the circuit is working. The efficiency is about 100%, the heat=
 sink
> becomes not even hand warm during a 30 min 300W carrier. The output
> power is at least 300W CW, maybe more is possible. I haven't tested=
 that
> yet.
>
> One hint: The VFO has to run before you push PTT. Otherwise one FET=
 is
> switching the whole time and the fuse will melt! There are several
> options that can be added to the circuit (e.g. current limiting,
> overvoltage protection, temperature regulated fan, SWR bridge...) bu=
t i
> wanted to keep it as easy as possible. There is an optional fiber op=
tic
> cable PTT input to totally decouple the PC from the PA. This also wo=
rks
> very sufficient.
>
> This circuit uses an ferrite output transformer of unknown material.=
 But
> it is not critical. Just try what you have, maybe with a power suppl=
y
> with current limiting. In that circuit, the current without a connec=
ted
> load is less than 150 mA (this makes it very suitable for /p operati=
on
> as well). If you try another ferrite core, you have to check for pro=
per
> primary turns number. If the number of turns is to less, the core wi=
ll
> go into saturation (with or without a load, so check it without a lo=
ad,
> just the primary winding). This can be seen either by watching the=
 input
> DC current or by watching the Drain-Source voltage. If it is in
> saturation, the rectangular edges/slope (falling slope) becomes roun=
d.
> Something between 2x 3...5 turns may be a good value.
> In my configuration the PA works from 8...100 kHz. increasing or
> decreasing the operating frequency is another way to check if the
> primary turns are optimal. I can give more detailed infos, if wanted=
 in
> a concrete case.
>
> The circuit handles reactive power without problems! This is the
> opposite to some audio amps ;-) Another advantage is, that the outpu=
t is
> isolated from the input.
>
> The PA works at 12V (11...14V) and can be used with batteries of cou=
rse.
> It needs the douple output frequency at the input, means you have to
> apply 17,94 kHz to get a 8,97 kHz output frequency. The input freque=
ncy
> should be rectangular with about 12Vp.
>
> Have fun and make the band alive ;-)
>
> 73, Stefan/DK7FC
>