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Date: Mon, 01 May 2006 01:13:23 -0700
From: Scott Tilley <sthed475@telus.net>
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Subject: Re: LF: RE: pictures of my new 136kHz stn
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Dick, Dave and LF Group

Using a design here with 4 FETs (W34NB20) in a module with the two pairs 
combined this nets about 900W with 37V input.

Now on the MO_ALFA we have 8 FETs in two modules of 4 arranged in pairs 
of 2 combined for 2KW and when loafing on the 'stun' setting  we're able 
to get 1200W+ without much heating at all, in fact she runs very 
cool(much more efficient then a single module running balls to the 
wall)... At 2KW forced air is a must... Nothing  paralleled and no 
traditional LPF required as the Wilkinson does the job and provides some 
port to port isolation.  

We could push for maybe 3KW as the 8x400W PSUs are loafing still...  But 
after the Tesla display when we commissioned it at 2KW in my backyard 
cooler heads prevailed...!

The highest voltage we can reliably push out a signal with without 
'strange' events is 41V.   However,  I run lower at 37V as a nominal 
safe choice.

I found the W34NB20 better in my application then the IRFP450...

73 Scott VE7TIL

G0MRF@aol.com wrote:
> In a message dated 30/04/2006 21:43:09 GMT Standard Time, 
> ganymede444@btopenworld.com writes:
>
>     Hi Dick, LF Group,
>      
>     What power supply voltage will you be using for your new TX, and
>     what RF power do you hope to get out with 4 times IRFP450?
>      
>     73, Dave G3WCB IO91RM
>
> Hi Dave / Dick.
>  
> If it helps:  I converted on of my 250W linear amplifiers which used 4 
> IRFP450s to class D(ish)  The power output went to 700W on 136kHz.  I 
> just replaced the input phase splitting transformer with the normal 
> class D 4426 driver chip.  
> I also used the same amp in Scotland at 300W on 73kHz to work Jim 
> M0BMU and Derek G3GRO who were nr Lands End. PSU was adjustable 35 to 48V.
>  
> Thanks
>  
> David  G0MRF