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

[Carl]

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 at telus.net>
To: <amps at 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 at audiosystemsgroup.com>
> Subject: Re: [Amps] Guidelines.....toroids for tank ckts
> To: amps at 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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