Date: Tue, 11 Sep 2012 19:56:04 +0200
From: uwe-jannsen@kabelmail.de
To: rsgb_lf_group@blacksheep.org
Message-ID: <14ee05b4a92d4fe191ab2561550f002a@kabelmail.de>
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Subject: Re: LF: Small "linear" medium wave PA
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Hello Wolfgang,
 thanks=2E
 I printed the diagram and the print made its way to the workbench=2E
 the next step will be in some weeks=2E=20

=A0GL=20

Uwe/dj8wx=20
  Von: rsgb_lf_group@blacksheep=2Eorg
 Gesendet: 10=2E09=2E2012 22:05
 An: rsgb_lf_group@blacksheep=2Eorg
 Kopie: rsgb_lf_group@yahoogroups=2Eco=2Euk
 Betreff: LF: Small "linear" medium wave PA

 Hello Uwe,

 I have completed the 2nd part of the circuit diagram of my small=20
 "linear" PA :

 http://www=2Eqsl=2Enet/dl4yhf/mf_reception/MF_Reception=2Ehtml#mf_line=
ar_pa

 You may have to reload the page (press F5) since it has just been uplo=
aded=2E

 IMO, the efficiency for this power range (50 =2E=2E=2E 60 watts in my =
case) is=20
 adequate=2E It's simple, and even when "slightly overdriven" it retain=
s=20
 the amplitude ramp of the keying signal from the driving transmitter (=
IC=20
 706 with 2 watts output on MF)=2E When driven to the clipping point, w=
hich=20
 is OK for CW, the amplifier drew just above 3 amps DC at 13=2E8 Volts =
to=20
 produce 30 watts of RF=2E At that power level, a small heatsink ("CPU=20
 cooler") is sufficient=2E

 With more turns on the drain output transformer, and a larger heatsink=
,=20
 even more power would be possible, possibly up to 100 watts (which I=20
 don't need at DF0WD)=2E

 The DC overcurrent protection is simple but effective: With the two=20
 transistors on the 2nd part of the circuit, the gate bias voltage is=20
 simply "pulled down" so the drain current and power dissipation stays =
in=20
 non-lethal limits (for the MOSFETs)=2E The 30 milliohms resistor is ju=
st a=20
 short piece of 'Constantan' wire=2E It is barely visible on the photo =
of=20
 the board, near the "DC current sense / limiter"=2E

 All the best,
 Wolf =2E
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<div style=3D"margin: 5px;padding:0;font-family: Arial; font-size: 13px=
;"><p><span style=3D"font-size: 13px;"><strong>Hello Wolfgang,<br />
<span>thanks=2E<br />
I printed the diagram and the print made its way to the workbench=2E<br=
 />
the next step will be in some weeks=2E</span></strong></span></p>
<p><span style=3D"font-size: 13px;"><strong><span>&nbsp;GL</span></stro=
ng></span></p>
<p><span style=3D"font-size: 13px;"><strong><span>Uwe/dj8wx</span></str=
ong></span></p>
<br />
<hr />
Von: rsgb_lf_group@blacksheep=2Eorg<br />
Gesendet: 10=2E09=2E2012 22:05<br />
An: rsgb_lf_group@blacksheep=2Eorg<br />
Kopie: rsgb_lf_group@yahoogroups=2Eco=2Euk<br />
Betreff: LF: Small "linear" medium wave PA<br />
<hr />
<br />
Hello Uwe,<br />
<br />
I have completed the 2nd part of the circuit diagram of my small <br />
"linear" PA :<br />
<br />
http://www=2Eqsl=2Enet/dl4yhf/mf_reception/MF_Reception=2Ehtml#mf_linea=
r_pa<br />
<br />
You may have to reload the page (press F5) since it has just been uploa=
ded=2E<br />
<br />
IMO, the efficiency for this power range (50 =2E=2E=2E 60 watts in my c=
ase) is <br />
adequate=2E It's simple, and even when "slightly overdriven" it retains=
 <br />
the amplitude ramp of the keying signal from the driving transmitter (I=
C <br />
706 with 2 watts output on MF)=2E When driven to the clipping point, wh=
ich <br />
is OK for CW, the amplifier drew just above 3 amps DC at 13=2E8 Volts t=
o <br />
produce 30 watts of RF=2E At that power level, a small heatsink ("CPU <=
br />
cooler") is sufficient=2E<br />
<br />
With more turns on the drain output transformer, and a larger heatsink,=
 <br />
even more power would be possible, possibly up to 100 watts (which I <b=
r />
don't need at DF0WD)=2E<br />
<br />
The DC overcurrent protection is simple but effective: With the two <br=
 />
transistors on the 2nd part of the circuit, the gate bias voltage is <b=
r />
simply "pulled down" so the drain current and power dissipation stays i=
n <br />
non-lethal limits (for the MOSFETs)=2E The 30 milliohms resistor is jus=
t a <br />
short piece of 'Constantan' wire=2E It is barely visible on the photo o=
f <br />
the board, near the "DC current sense / limiter"=2E<br />
<br />
All the best,<br />
Wolf =2E<br /></div>
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