[Amps] Guidelines.....toroids for tank ckts

[Jim Thomson]

Date: Sat, 24 Mar 2012 16:08:13 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
Subject: Re: [Amps] Guidelines.....toroids for tank ckts

On 3/24/2012 3:24 PM, Carl wrote:
> I would not recommend toroids above 40M and even there its iffy at high
> power. And of course use one per band.

Yes. I don't know anything about powdered iron materials, but all 
ferrites get increasingly lossy with increasing frequency. A few 
ferrite mixes are designed to handle high power, and are pretty low loss 
at low to medium frequencies, but each of them has a high frequency 
limit, beyond which their loss has increased to the point that they are 
not very useful. For example, Fair-Rite #61 starts getting lossy above 
about 10 MHz, while their #67 starts above 20-30 MHz. In general, 
losses will couple from the core to the wires, and will show up in the 
equivalent circuit as resistance.

Another issue is voltage breakdown -- ferrites are semi-conductors, and 
each mix is different there too. Some are pretty good insulators, others 
are fairly conductive. It's worth studying the Fair-Rite catalog, which 
is really excellent. Fair-Rite data sheets include data for resistivity, 
permeability and permittivity.

##  U can’t use any ferrite product for HF tank circuits.  The only thing that
works is  #2  red core..powdered iron..and lots  of it.   2-3  stacked
T-225-2A  cores..each 1” thick  for a total  of  2-3” thick is the answer.
The .5” thick versions  will work..but run hot..depending on duty cycle. . 



If you have a solid EE background, it's 
also worth calling Fair-Rite's technical support people. But study their 
catalog and applications notes first so that you know what questions to 
ask and can understand the answers.

##  Try that sometime.   “what  type, and what size, qty,  of either ferrite
or powdered iron do I require for a 2-5 kw output amp,
for 1.8-7 mhz”       They won’t even know what you are talking about. A lot of these
“applications engineers”   are abt one step above a salesman.   Most don’t have any practical
experience with the products they sell.   Marv  calculated the power dissipated..running 1.5 kw CCS
out, using type 2 powdered  iron cores....and it was aprx 57 watts...regardless  of whether  1-2-3-
cores used.   Now that’s a bunch.   Emtron had enough problems with their big amps..and torroids. 
They hit a whopping 226 deg C..when  you point a fluke IR  point and shoot thermometer at em...
running full bore cxr. 

##  #2 mix..red ones are fine... but u need the total  weight of em to be enough to handle the power involved. 
stack 2-3 small ones..or use a bigger diam one.  get em cooking..and their uh will drop.  Then the tuning is way
off.  It will  go non linear too.   Unless  you have space constraints, use air wound coils  from wire or edge wound ribbon. 
They run stone cold. 

Jim   VE7RF  




73, Jim K9YC