Date: Sat, 24 Mar 2012 16:08:13 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [Amps] Guidelines.....toroids for tank ckts
To: amps@contesting.com
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. 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.
73, Jim K9YC
## You CAN’T use ferrites for tank circuits. They will blow up in your
face asap.
## Also, when using stuff like T-225 torroids, beware they come in two
different thickness.
T225-A and also T225-2A Both are 2.25” OD. If you lay em both on the
table, with the
hole facing the ceiling-floor, the A version is only .5” thick. The 2A
version is 1” thick.
## I used three T225-2A’s stacked on top of each other, then the usual tape
etc, then wound
em with 10 ga polyimide magnet wire. That stuff is good for 15 kv. 930 kv
between turns)
That assy was used to get a 80-10m amp to work on 160m. The t225-a and 2a
are powdered iron material, and #2 mix,
and red in colour. .
## the entire mess ends up being 2.25” diam x 3” long..and that’s b4 the
wire is added. It also
ends up heavy. My conclusion is, a piece of air-dux, wound with 12 ga, does
the same job, and at a fraction
of the weight, hassle. I found several air dux coils in my collection, and
noticed that one of em had the turns a lot closer
then the others, yet both had the same OD and wire ga. The closer spaced
stuff was ideal for low band tank circuits,
as it provide more uh per unit of length.
## If you design it right, and keep the uh a bit on the high side, you will
reduce the loaded Q of the tank circuit, that means
less tune and load C.. and also broader tuning. Circulating current is way
less, and the coil runs stone cold.
## Tororids are a pita. I avoid em like the plague. But if u do use em, 3 x
T-225-2A’s stacked will handle 1.5 kw rtty
on 160m.
later... Jim VE7RF
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