[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
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