Message-ID: <15c1258d892.marcocadeddu@tin.it>
Date: Tue, 16 May 2017 19:40:31 +0200 (CEST)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: R: Re: LF: RE: Combining LF amps revisited
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Hello Chris,

happy to read that increasing the turn number you can make the life 
easier to the toroids ;-) (the FETs also enjoy hi).
I'm not a professional, but using the formula and taking 
care of respect of the Bmax of 0.1T, I had (up o now) no problems with 
xformers. Since some years I switched to  Epikote forms wich are 
looking better for low frequencies (and here in Italy are also cheaper 
of Amidon cores).
In the weekend I should start some trials with simil Decca approach: 
the PS at 180Vdc is already running and could be later transformed in 
direct rectification of the main aiming to 1kW which should then allow 
to reach the 1W. Still running 250 or 20W on LF with satisfactory 
resoult considering the city antenna and the season :-)

73, Marco IK1HSS
----Messaggio originale----
Da: dead.fets@gmail.com
Data: 16-mag-2017 17.29
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: R: Re: LF: RE: Combining LF amps revisited


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