From: "Dave G3WCB" <ganymede444@btopenworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 1 Mar 2005 11:13:00 -0000
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Subject: LF: Big Bad Amps <was re: ... --- ...>
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Hi, Scott.

If you're into Big Bad Amps, you should check out G4FTC's site
http://www.qsl.net/g4ftc/amplifiers/136khz/home.htm He describes a 3kW LF
amp. that uses 8 x IRFP450's in a bridge arrangement. Biggest PA I've seen
so far!

BTW, if you have two identical TX's already, and you find the Wilkinson
thing doesn't work out, you could re-configure your amps. into a bridge
arrangement instead, bit like the Decca TX's.

Keep that fire-blanket handy!

Cheers,

Dave G3WCB.

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Scott Tilley
Sent: 01 March 2005 10:59
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: Re: ... --- ...


Hey Alan

We got the bugs out...  Once I found the problem with the lack of sinc in
the 4013 divider stages things have been working as expected.  I thought
about the inductor coupling; however, based on my observations the combiner
is not doing anything negative to the signal train.  We still have >80% eff.

I would like to try this with toroids next and compact it down.  I'm also
dreaming up a bigger badder amp using this concept.  It seems real stable
and doesn't require running the system 'balls to the wall' to get some
serious power from 4 FET and a reasonable PSU voltage.

73 Scott

----- Original Message -----
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, March 01, 2005 2:49 AM
Subject: LF: Re: ... --- ...


> Hi Steve I have just had a thought your construction looks fine....BUT
maybe
> the two coils are too close together and there is some coupling. I wonder
if
> it is possible to temporarily turn one at right angles to kill any
coupling
> and see if that helps??
> The biggies in my Web page were made with big toroids I believe probably
> iron dust rather than ferrite, as the inductance reqquired is not that
high
>
> Cheers de Alan G3NYK
>
> ----- Original Message -----
> From: "Scott Tilley" <sthed475@telus.net>
> To: <lowfer@lwca.org>; <rsgb_lf_group@blacksheep.org>
> Sent: 01 March 2005 06:51
> Subject: LF: ... --- ...
>
>
> The smoke test of this Wilkinson Combiner was successfull in that no smoke
> came out and nothing died.  However, we get enough heat to cook an egg on
> the 100ohm balance resistor.
>
> We have a scope match on the output to the dummy load and it shows about
> 225W from one transmitter, add another and we get 450W, success NOPE!  The
> transmitters are outputting ~450W each! Therefore, half the power is being
> absorbed in the 100ohm balance resistor.  Examining the phase relationship
> of the input to the combiner waveforms indicates they are in phase within
> ~10degrees and almost equal in amplitude.  So what gives!  Anyone have
some
> idea what may be going wrong?  Of course we have checked and doubled
checked
> the circuit for errors and nothing...  All seems as it should according to
> formulas and drawings we have viewed and designed it from.
>
> Does anyone have an idea how we could troubleshoot our way through this?
>
> Any advice would be appreciated.
>
> 73 Scott and Steve(It's all his fault ;-)
>
>
> Check the status of radio beacon 'TIL'  in CN89lg at:
> www.scottboxx.com/radio
>
>
>
>