Message-ID: <15c11b55a0f.marcocadeddu@tin.it>
Date: Tue, 16 May 2017 16:41:56 +0200 (CEST)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: LF: RE: Combining LF amps revisited
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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

----Messaggio originale----
Da: andy.g4jnt@gmail.com
Data: 15-mag-2017 14.42
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: LF: RE: Combining LF amps revisited

For transformers the core is not terribly critical provided you use a 
grade
of ferrite designed for the frequency of interest.  And at LF that 
means
SMPSU cores

If I see a certain size core being used in a 500W SMPSU then there's a
pretty good chance a core of the same size is going to work OK in an LF 
Tx
of the similar rating.   No data sheets or trying to work out 
temperature
rises.

I just use whatever feels right and apply the V < 4.44F.N.A.B  
absolutely
rigorously, keeping B to less than 0.1 usually

As for impedances:  well they're  just Z1/Z2 = SQRT(N1/N2)
Use V = 4.44.F.N.A.B to give you turns min, then calculate N1 and N2 
while
meeting that criteria

Andy  G4JNT

On 15 May 2017 at 11:59, Chris Wilson <dead.fets@gmail.com> wrote:

> Hello Clemens,
>
>
> Thanks  for  the  reply, the 3 stacked cores will rise to 70 degrees 
C
> plus  even with a small computer processor fan blowing through them. 
I
> am  investigating  ways  of  reducing  this, the cores are shown as 
77
> material  in  jay's  schematic,  but  he  and I are using the newer 
78
> material  for the PA output transformer cores. I may try using this 
76
> material  in  the  combiner transformer. Someone else suggested 
making
> the   PA   output   transformers   work   at  100  ohms  and  using  
a
> transformer less  zero  degree  hybrid  coupler.  I'd  try  Andy's 
twin
> primary,  one  secondary  transformer instead of the coupler if i 
knew
> what winding ratio and what core to start off with. Thanks again.
>
> > Hi Chris,
>
> > I have a tool by DJ5IL here which predicts around 60°C for the 
cores
> > (excluding heat caused by the winding)
> > and ca. 480 Gauss flux density.
>
> > 73
> > Clemens
> > DL4RAJ
>
>
>
> --
> Best regards,
>  Chris                            mailto:dead_fets@gmail.com
>
>
>