[Amps] 50ohm:200ohm toroidal transformer

[R.Measures]

On Mar 22, 2005, at 9:07 AM, gdaught6 at stanford.edu wrote:

> Hi all,
>
> I'm trying to build a 50:200 ohm broadband transformer for the input
> of a tetrode amplifier.  Sevick's book and Measures' website give
> instructions for such a 2.4 inch unun.  Sevick says it can handle
> over a kW: I only need a 100W job.

George -- I used a 2.4 inch core because it was large enough to wind 
myself without having to hire a lepruchuan.  The amount of extra money 
spent for the 2.4" core is minimal.  A caveat -- If the amplifier is to 
be used above 10MHz, a Mu=40 core is preferable because Mu=125 cores 
begin to saturate c. 13MHz.  In my experiences, sellers of ferrite 
cores and sellers of automobiles are comparable in truthfulness.

> The ARRL handbook says a 1.5 inch
> version will handle over 100W.  Does anyone have a "recipe" I could
> follow to make such a thing?  Requirements are:
>
> a) 50 Ohms to 200 Ohms
> b) 3-30MHz
> c) low loss (I don't want it heating up and self-destructing)
>
> What core material and what size should I use?  What is the best
> place to get one (or two) of the cores? What wire and how many turns
> should I use?
>
> I readily confess that I'm woefully knowledge-and-understanding-
> deprived in this area!
>
> Thanks in advance for any help!
>
>
> 73,George T. Daughters, K6GT
>
>
>
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>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org