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Re: [Amps] What to buy?

Subject: Re: [Amps] What to buy?
From: Jim Barber <>
Date: Fri, 04 Feb 2011 10:28:38 -0800
List-post: <">>
A while back I went through the calcs in the Amidon reference book 
trying to find a way to stack a bunch of Mix 2 powdered-iron cores for 
the 160m "helper" inductor in a legal-limit project.

I don't remember the specifics of the tank offhand, but I do remember 
that no matter how I juggled things I couldn't come up with a stack that 
would hold up without overheating under at least some of the conditions 
I set up. Those conditions include 50% overload for tune-up purposes, so 
I suppose you could say that it was a self-fulfilling expectation that 
it would fail. So be it - in a conservative design where size, weight 
and noise (and WAF) aren't the primary considerations I believe 50% for 
tuning and occasional mis-tuning is reasonable.

My .02,
Jim, N7CXI

On 2/3/2011 4:02 AM, Jim Thomson wrote:
> Date: Mon, 31 Jan 2011 10:52:57 -0500
> From: "Carl"<>
> Subject: Re: [Amps]To: What to buy?
> Hmmm, ferrite has never been recommended for RF tank circuits that Im aware
> of. Ferrite is fine in receiver and other low level applications mostly at
> low frequencies.
> Good amplifier engineering has used powdered iron in various mixes,
> generally from Micrometals in North America.The #2 mix is the usual choice
> in amps for 160-80M and has been in use since the late 70's.
> There are huge differences between the 2 materials in regards to losses and
> temperature stability.
> Carl
> KM1H
> ----- Original Message -----
> From: "Jim Brown"<>
>>> How are things different in a transmitter's resonant circuits?  First,
>> we want to minimize loss, so we (should) use low loss cores (like
>> Fair-Rite #61 or #67). These are NiZn cores, and have much lower mu than
>> those designed for RFI suppression (like #31 and #43).
>> Inductors wound on #61 or #67 can have Qs on the order of 10 or more,
>> and are typically self-resonant a bit above HF.
>> Note also that my work has focused on ferrite materials, NOT powdered
>> iron.
>> 73, Jim Brown K9YC
> ###  Ferrite  would not last more than 30 x seconds in any tank circuit, in
> any HF amplifier.  Type #2 mix [ red cores]  powdered iron cores are what is
> normally used.  Beware that there are TWO types of T-225 cores... lableled
> 225-2A   and  225-2B.    The A version is only 1/2" thick.  The B version is 
> 1" thick.
> ## For 160m use.. typ 3 x 225-2B's  are stacked... so the entire mess ends up 
> being
> 2.25" OD  x 3"  long..and very heavy.  That's before you add the wire.  I 
> modified one
> of my hb amps..and added 160m to it.  It was a lot easier to just use a small 
> piece of
> air-dux with 12 ga wire.. vs  3 x torroids.   Interesting enough, I found 
> some air dux
> that was 12 ga... but with slightly closer spaced turns  vs the 'normal 12 ga 
> airdux'.
> Now this stuff worked ideal for 160m...since it was used on 160m only.
> ## The original 80-10m rf deck now is 160-10m.   The new close spaced 12 ga 
> air-dux
> coil was the ideal ticket.  Weighs virtually nothing..and ZERO heat.  The 3 x 
> torroid
> approach weighs a ton..and dissipates aprx 57 watts.  2 x torroids will also 
> dissipate 57 watts.
> ## I have given up on torroids  for tank coils on the low bands. I have found 
> some small diam, edge
> wound ribbon coil stock that works the best for low band work.  3/8" edge 
> wound ribbon [.072" thick]
> is the same as .28"  tubing for current handling.   1/4" ribbon [ also .072" 
> thick]  is ample in most cases
> and is the same as .2" OD tubing.   A friend also gave me a bunch of air 
> dux.. that uses 8 ga wire.. and the
> wire was copper..and not the usual tinned material.  These are things of 
> beauty. I didn't know you could
> get coil stock in 8 ga wire.
> Jim   VE7RF
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