The T225-2 is the one Ive preferred for decades as for very little
additional money it has a substantially larger volume to dissipate heat
compared to the T200 size which seems to usually be the frugal hams choice.
There is no difference in inductance within the usual 20% tolerance range.
The T225A-2 is the double height version.
Ive a few hundred of the T225-2; email me direct for a price much less than
Amidon, etc. Include a Zip code and I also ship worldwide.
Carl
KM1H
----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Sunday, March 25, 2012 6:55 AM
Subject: [Amps] Guidelines.....toroids for tank ckts
> 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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