Date: Sat, 24 Mar 2012 16:08:13 -0700
From: Jim Brown <jim@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
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