[Amps] What to buy?

[Jim Thomson]

Date: Mon, 31 Jan 2011 10:52:57 -0500
From: "Carl" <km1h at jeremy.mv.com>
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" <jim at audiosystemsgroup.com>

>> 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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