From: Chris Wilson <dead.fets@gmail.com>
Date: Tue, 16 May 2017 16:29:29 +0100
Message-ID: <1009577925.20170516162929@gmail.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <15c11b55a0f.marcocadeddu@tin.it>
References: <15c11b55a0f.marcocadeddu@tin.it>
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Subject: Re: R: Re: LF: RE: Combining LF amps revisited
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Hello Marco,
16 May 2017

Good  to  hear  from  you,  thanks  for  the  reply. I have remade the
combiner's  output  transformer using 3 stacked 78 material toroids of
the same size, and wound it with 180 strand speaker wire, pure copper,
with  an inner conductor of about 2mm diamter. I wound 3 times as many
turns, 15 on the primary, 21 turns on the secondary. It now runs about
40 degrees Celcius with no fan cooling, and the drain wave forms are a
lot  less  spiky.  I  saw  fair-Rite  now list a 98 compound, and it's
advertised  as  a  big  improvement  for  the  frequency  than  the 78
material,  but  there's  an error on their web site and 98 compound is
not available in toroidal form, unfortunately. I did see this beast in
78  compound  though, a lot bigger than the FT-240 cores, and wondered
if the fairly high cost is worth it?

http://uk.rs-online.com/web/p/ferrite-rings/4956317/

Thanks again!


> Chris,

> I guess there is a little misstyping in the calculation performed from
> Clemens on the DJ5IL tool....
> he entered 2.5 instead of 25 in the impedance box: the primary 
> winding after the combiner should work on 25 ohms. If you enter 25 ohm
> the flux rise a lot beyond the saturation of the 3 stacked cores and 
> therefore they have all the rights to warmup!
> On the other hand if you apply the Bmax formula given from Andy, the 3
> stacked cores have A of 471mm²
> and with 2kW of power on 25 ohms the minimum number of turns on the 
> primary should be 8 not 5.
> So one more turn to keep B below 0,1T and you should run more 
> confortable with N1/N2=9/13
> 73 de Marco, IK1HSS


-- 
Best regards,
 Chris                            mailto:dead_fets@gmail.com