Re: Homemade chokes

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

On 10 Aug 00, at 12:18, Tesla list wrote:

> Original poster: "acmnovak" <acmnovak-at-email.msn-dot-com> 
> 
> Hello everyone,
> This is like the fifth post from me today. Geez...
> Anyhow, I was wondering if one could make an effective RF choke using a
ferrite
> flyback core. I used these for chokes in crossovers for subwoofers which
worked
> fine, but I am somewhat concerned about the power handling capabilities of
> these. The cores are are about 2" x 2" (5cm x 5cm) with a core diameter of
> about 0.4inch (1.2cm). I wound one with 22 guage wire which I salvaged
from an
> old ignition coil primary (oil submersed type).  If you look closely at an
> audio crossover circuit, you'll notice that it is very similar to a RF
> protection circuit in a Tesla Coil. It has a choke which only allows low
> frequency ac to pass through, unimpeded, and a capacitor in series with the
> tweeter, which high frequency signals use as a low resistance path to
ground. 

You can - but watch for core saturation (a function of NI and 
core area and material) if the core is ungapped.
  
> Also, Does anyone know how to determine a circuit's Q?  I read somewhere
that a
> Tesla Coil's primary and secondary coils should have an equal Q. If this is
> true, we should be able to determine the exact numbet of primary turns
needed.
> Right?

It is a fallacy. Primary Q varies with primary voltage so the 
Q's can be equal at best at just a few instants when primary 
voltage and currents are a particular value (which depends on 
primary surge impedance). Secondary Q is essentially constant 
until a discharge issues forth. For maximum efficiency, get 
the peak primary currents to a low value.

Regards,
Malcolm