Re: LF: TX Toroid Material

[DK7FC <selberdenken@posteo.de>]

Hi,

I took a FT-240-77 in my large PA a while ago. The primary winding can 
be seen here:
https://dl.dropboxusercontent.com/u/19882028/MF/20130713_002528.jpg
47 turns were fine to switch a 475 kHz (nearly) rectangular signal with 
an amplitude to 320 V. From that, you can calculate the number of turns 
you will need. Let me think: A sine wave causes a lower peak flux in the 
core, so you are on the safe side. So you are on the safe side. 230V rms 
for 47 truns. If you want to run 300W at 50 Ohm, that's U=sqrt(P*R)= 78V 
rms, i.e. 47*78/230= 16 turns for the secondary winding. If your primary 
side is at 2.1 kOhm, you need sqrt(2100/50)*16 = 104 turns. You can use 
thin wire on the primary side. 104 turns is managable and the losses in 
the transformer will be low! A series C (1 uF MKP-10 1.6 kV maybe) to 
the primary winding may be needed to decouple DC. Then you are down at 
50 Ohm and can use the well known double-pi LPF designs using 6.8 nF 
(-j50 Ohm) and 16.7 uH (j50 Ohm)... For further calculations are needed. 
Beware of simulations! :-)
73, Stefan

Am 17.10.2015 20:50, schrieb phl@netikka.fi:
> Hello Ken,
>
> For transformers I have used Amidon -77 ferrite material successfully 
> on 136 and 472 kHz. Same goes for Ferroxcube 3F3 ferrite material.
> For inductors in filters or chokes the Amidon -2 iron powder mix as 
> suggested by Stefan has worked well for me on 472 kHz and I have seen 
> it used in many working 136 kHz designs too.
>
> For matching a 2 kohm anode impedance to 50 ohm using a ferrite 
> transformer I would be very careful, you will really have to calculate 
> the number of turns and get it right in order not to saturate the core 
> since the voltage swing is large at the 2 kohm level at those powers. 
> At least this is my humble non-professional opinion on the subject.
>
>
> BR
>
> Paul-Henrik, OH1LSQ
>
>
>
>
> Quoting Ken <ken.h.wright@btinternet.com>:
>
> > Hi Stfan.
> >
> > I have been looking at the 77 type material, but waiting for other group
> > members opinion.
> >
> >
> >
> > 73
> >
> >
> >
> > Ken
> >
> >
> >
> >   _____
> >
> > From: owner-rsgb_lf_group@blacksheep.org
> > [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of DK7FC
> > Sent: 17 October 2015 17:02
> > To: rsgb_lf_group@blacksheep.org
> > Subject: Re: LF: TX Toroid Material
> >
> >
> >
> > PS: For the RF transformers i often use N30 ferrite material with good
> > results. An AL of 4000 nH or above is a good choice. If you want to use
> > Amidon ferrite cores, use type 77 material (available on most 
> > distributors).
> > 73
> >
> > Am 17.10.2015 17:41, schrieb Ken:
> >
> > Dear All. I am having problems with the choice of material for the 
> > output
> > network of the 475kHz Valve TX. The network is an L - C - L, 'T' network
> > with an input impedance of 2100 ohms and a load of 50 ohms, for this
> > configuration the input L is 7.7mH, shunt capacitance is 117pf, and 
> > output L
> > is 1.1mH. The PA design using a 6146 low power or 813 high power work 
> > fine
> > when simulated using LT spice IV. When testing in the real world 
> > using the
> > 6146 there is in excess of 800v rms rf on the network side of the anode
> > coupling capacitor, but nothing after the input L. I can only 
> > conclude that
> > I using the wrong type material for the toroids, I used the largest size
> > (unmarked) toroid which gave me a modest number of turns. I have 
> > checked the
> > Amidon tables and Iron Powder because of the low AL values, which leaves
> > Ferrite, which mix would you recommend? The simulations give me output
> > powers 90W for the 6146, and 300W for the 813. I would be grateful 
> > for any
> > core material advice .
> >
> >
> >
> > Ken Wright.
> >
> > M0KHW