Fw: [KLQRP] Pixie 3? - - - Take 2

[Gary Oneil]

Sir Darwin;

        I've re-thunk this a bit, and discovered I misled you on the Diode 
polarity. It should be the same polarity as shown. It would have no effect 
if you did this as I originally suggested. You may have to tweak the 
resistor values around the TL-431 a bit also to get this to work without 
distorting much. Adding another transistor would be a better solution, but 
that starts to rob it of its simplicity. :-(

72


Regards;

Gary E. O'Neil
Nova x4  Usage & Applications
PPC Applications Engineering
3039 Cornwallis Road, 062/E112
Research Triangle Park, NC  27709
 
Home Office:   (919)-859-4902
   RTP Office:   (919)-543-5750    T/L 441-5750
    Cellphone:   (919)-522-5460

Ferdinand Porsche may have been inspired by elephants when he designed the 
Volkswagen. Slow but reliable transportation. with a trunk in the front.
----- Forwarded by Gary Oneil/Raleigh/IBM on 11/22/2007 12:55 AM -----

Gary Oneil/Raleigh/IBM
11/19/2007 11:21 PM

To
"Piatt, Darwin" <dpiatt at fnni.com>
cc
klqrp at knightlites.org, klqrp-bounces at knightlites.org, raymcn at gmail.com
Subject
Re: [KLQRP] Pixie 3?





Greetings Sir Darwin;

        This looks pretty sweet.... it nearly makes me want to go back and 
do a re-spin of our KnightSmite. :-)

        Looking this over, I've got a couple of things you might want to 
experiment with.

        The easiest one first... add a 150 pF cap in parallel with L3... 
It then acts as a trap between the 2nd and 3rd harmonic and will bring 
your transmit spurs down a good bit more than just the simple PI network. 

        The second one I'm less certain about, but its certainly worth 
attempting.  Remove diode D1, and add it across C8 with the anode at the 
top (opposite polarity shown in your schematic). You can likely do away 
with R5 and C10 altogether also, and simply connect the top of the 68 ohm 
resistor directly to 9 V.

        Two new behaviors I would expect with this new configuration are:

        1) you will likely hear clicking in the speaker during keying... a 
not too unpleasant sidetone, which would be a welcome new feature. :-) 

        2) The TL-431 cathode will be driven to 6 Volts during keying 
virtually shutting it down so that it doesn't draw any significant current 
while in the transmit mode. If this works as I anticipate, this will be 
much nicer than shorting the 6 Volt rail as your current design does... as 
well as all Pixie derivatives do with the LM-386. It is this feature of 
using the TL-431, in addition to the unconditional audio stability that 
prompted my recommending this for the Pixie application in the first 
place. If this works as I suspect it will, you will likely never see a new 
Pixie incarnation using an LM-386 to drain their batteries. :-)

        Give this a whirl and keep us posted on how it works out for you. 


Regards;

Gary E. O'Neil
Nova x4  Usage & Applications
PPC Applications Engineering
3039 Cornwallis Road, 062/E112
Research Triangle Park, NC  27709
 
Home Office:   (919)-859-4902
   RTP Office:   (919)-543-5750    T/L 441-5750
    Cellphone:   (919)-522-5460

Ferdinand Porsche may have been inspired by elephants when he designed the 
Volkswagen. Slow but reliable transportation. with a trunk in the front.



"Piatt, Darwin" <dpiatt at fnni.com> 
Sent by: klqrp-bounces at knightlites.org
11/15/2007 03:22 PM

To
klqrp at knightlites.org
cc
raymcn at gmail.com
Subject
[KLQRP] Pixie 3?






So ok, one of the 'Sir' dudes suggested we replace the LM386 with the
TL431 (for fun) so here is the diagram of our 'work in progress'.
We will yell when it works?
If the list will not allow attachments, I will try to figure out how to
post it..
Dar...

Ain't this fun...

Darwin (Dar) Piatt - W9HZC
Midwest HomeBrewer's and QRP Group
http://www.qsl.net/hbqrp 
NAQCC # 1571
Polar Bear #9 - QCWA # 31632 
Flying Pigs # 936 - Zombie #826
GQRP - Iowa QRP Group
QRP ARCI # 11966
10-10 Webmaster (#73090)


[attachment "pixie3.jpg" deleted by Gary Oneil/Raleigh/IBM] 
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