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From: "Dave G3WCB" <ganymede444@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Date: Tue, 2 May 2006 21:10:18 +0100
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Subject: LF: RE: pictures of my new 136kHz stn (IRFP450)
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Hi Scott, David and Dick, LF Group,

Thanks for the helpful comments. It seems that 400W out with 37v supply
would be a reasonable target for my next winter project. My current rig
gives 200W output from a pair of SMM70N06 FETs at 15VDC.

The STW34NB20 FETs are cheaper than the IRFP450, but I see that Farnell will
be no longer stocking them, and are recommending the Fairchild FQA55N25 as a
replacement. This is rated at 250V/55A, and might be an even better choice.

Scott, has your home-page moved? The Scottboxx link no longer seems to work.

73, Dave G3WCB IO91RM

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Scott Tilley
Sent: 01 May 2006 09:13
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: pictures of my new 136kHz stn


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