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
Da: [email protected]
Data: 16-mag-2017 17.29
A: <[email protected]>
Ogg: Re: R: Re: LF: RE: Combining LF amps revisited
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?
> I guess there is a little misstyping in the calculation performed
> 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
> 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
> 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
Chris mailto:[email protected]