----- Original Message -----

Sent: Wednesday, May 18, 2005 3:43 PM

Subject: LF: cores

Hi All

Another anomaly about these ferrite transformers. I wound a 3c type core with a Sec of 24 turns and measured it to be 1.38 mh then over wound this with the prim of 8 turns, this reduced the Sec to 982 uh with a prim of 110 uh. The ratio is about right x9 for a 1:3 ratio. I suppose meaurements should only be made when the transformer is complete with all windings, but it does show the effects of multiple windings over a single layer.

Except one has a lot of test equipment it seems most dabblers are working in the dark especially at LF, no wonder there are so many BANGS especially the FETS!!!!!!!1

To guarantee a robust no bang amplifier maybe TUBES are still the best bet.

From messages received it appears to be that as long as the ratio Prim /Sec is correct the ferrite material is not important but then why such a variety of different core material, although I do realise that certain other ccts at HF work better with a particular core mix.

I could do with some design literature written by others that have experience in the ferrite transformer research field.

73 de Mal/G3KEV

Hi Mal!

You do not tell how you measure inductance.

First, you can be absolutely sure that in a reasonably well designed transformer

(negligible leakage) the inductance ratio will always be equal to the square of the

turns ratio.

When it comes to measuring inductance, things are quite complicated. The

core permeability is not constant with frequency, but varies quite a bit. In ferrite

catalogues you will find a term called the complex permeability. The real

component of this term is what gives you inductance whereas the complex

component represents losses. Thus the inductance reading you find is dependent

e.g. on the test frequency of your inductance meter. In particular, if your test

frequency is high, you are really bad off! With a high test frequency, winding

capacitances may come into the picture, too.

A tip: Measure inductance with a test bridge at a low (much lower than 136 kHz)

frequency and make allowance for the complex permeability, -- or make your

measurement at 136 kHz (test set up: generator - inductance - variable resistor,

meter and a 3-dB criterion).

73=

Niels/OZ8NJ+