Re: LF: RE: Combining LF amps revisited

[Andy Talbot <andy.g4jnt@gmail.com>]

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