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Date: Wed, 12 May 2010 16:59:06 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Re: 12V/300W VLF PA circuit
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Hi Alan,

The ICL7667 is a double FET driver (inverting!):=20
http://www.datasheetcatalog.org/datasheets2/14/147008_1.pdf
So, if the both Qs are high, the outputs/gates are both grounded. You=20
just have to be sure that the VFO is connected before pushing PTT, as i=20
mentioned.
It was rather my goal to built an easy and well working circuit without=20
to much protection circuits, than building the "perfect" PA in a 6RU 19=20
zoll Rack with a loud exhaust and 50% efficiency (like many HF amps) ;-).
There has never occurred a fault with this PA yet. There is still the=20
first pair of FETs in use ;-)

73, Stefan/DK7FC


Am 12.05.2010 15:42, schrieb Alan Melia:
> 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 remove=
d.
> See the 136 PAs by G3YXM and G0MRF for keying ideas.....they key the sup=
ply
> 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 -----
> 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
>
>
>   =20
>> 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 experiments=
.
>> 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 sin=
k
>> 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 tha=
t
>> 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...) but=
 i
>> wanted to keep it as easy as possible. There is an optional fiber optic
>> cable PTT input to totally decouple the PC from the PA. This also works
>> very sufficient.
>>
>> This circuit uses an ferrite output transformer of unknown material. Bu=
t
>> it is not critical. Just try what you have, maybe with a power supply
>> with current limiting. In that circuit, the current without a connected
>> load is less than 150 mA (this makes it very suitable for /p operation
>> as well). If you try another ferrite core, you have to check for proper
>> primary turns number. If the number of turns is to less, the core will
>> go into saturation (with or without a load, so check it without a load,
>> just the primary winding). This can be seen either by watching the inpu=
t
>> DC current or by watching the Drain-Source voltage. If it is in
>> saturation, the rectangular edges/slope (falling slope) becomes round.
>> 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 output=
 is
>> isolated from the input.
>>
>> The PA works at 12V (11...14V) and can be used with batteries of course=
.
>> 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 frequency
>> should be rectangular with about 12Vp.
>>
>> Have fun and make the band alive ;-)
>>
>> 73, Stefan/DK7FC
>>
>>     =20
>   =20