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To: [email protected]
Subject: Re: LF: CORES
From: "Scott Tilley, VE7TIL" <[email protected]>
Date: Tue, 17 May 2005 12:26:40 -0700
Delivery-date: Tue, 17 May 2005 20:27:12 +0100
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#3 still has atleast enough inductance to have a reactance 4-5 times that of reflected resistance of a typical xfmr used in LF setups... Imagine the two impedances in // as the inductive reactance increases on the smallest winding it has less and less of an effect on the system... I would imagine that your resistance on the drive side is lower then 3 ohms and your inductive reactance would be in the 20 ohm range which is well within typical folklore for building such a beast... The best situation would be to choose one of the cores for the least number of turns needed to setup the match and still maintain an inductive reatance on the smallest winding of atleast 4 times the desired reflected resistance... The latter produces the most effecient system due to skin effect losses... Watch for saturation with the street ferrite as you hammer it hard... You're into the hair splitting realm...
73 Scott

Quoting hamilton mal <[email protected]>:

I have been winding some transformers recently and have been getting some odd
All cores have a prim of 9 turns and 27 turns sec.

1. 3C85 58 mm diam Prim inductance 167uh Sec 744 uh
2. Same material abt same size but E core Prim 292 uh Sec 2810 uh no gap.
3. Material unknown out of a smps similar size Prim 21 uh Sec 178 uh no gap
4. TV lopt core again abt same size Prim 79 uh Sec 865 uh no gap

The Prim wire is litz 2mm and sec 1mm copper enam wire in all cases.
1 and 2 seem to have a big difference considering the same material, 3 must
have a low u.
Has anyone else tried comparisons of cores.
If cores are selected at random and not checked there would be a big
variation in results even using the same turns ratio.
The above are intended as output matching transformers in the FET amps like
the YXM and MRF class D/E design.
I normally use 1 in my amps but have tried 3 and in spite of the big
difference in values it does seem to work and I have not noticed any
difference in RF output, which seems strange.
73 de Mal/G3KEV

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