See below,
*********** REPLY SEPARATOR ***********
On 3/31/05 at 7:39 PM Dr. William J. Schmidt, II wrote:
>Of course you realize that running the DC through the transformer is
>disadvantageous because it creates a strong "B" field in the core which
>can
>drastically reduce the dynamic response of the DC/RF transformer.
I take it "B field" meaning the maximum flux density or Bmax? Once Bmax is
reached, the waveform becomes distorted anything over this maximum flux
density. The permeability drops off sharply here too. The trick is to design
the core so it wont saturate at maximum power.
>With an
>outboard choke, both parts can be smaller in size... and keep the RF
>transformer from saturating (reduce non-linearities and less distortion
>because of it!).
This I dont understand as the same amount of DC current will still flow through
the windings of the RF transformer if the DC is fed to its center tap like in
all designs. Or are you speaking of connecting a choke to each collector where
only RF would be handled by the transformer? Youv'e lost me here on the
explanation.
>
>Most of us use another core as a DC choke... and AC couple the RF
>transformer... and there are better materials to use...
Actually, I think Palomar and others recommend 61 material in place of 43 for
2-30 MHz. For iron powder, color red is the one most used. I know in the
Motorola texts, Helge recommended a minimum permeability of around 800-900 if I
recall, but 61 is way lower. When maximum power is used, the 43 will heat up
quicker than the 61 or what I was told by Palomar. Once you fully saturate
ferrite and heat it to a certain point, the core is ruined and has to be
replaced. Something about the heat destroys its properties.
>
>
>Sincerely,
>
>Dr. William J. Schmidt, II K9HZ
>Trustee of the North American QRO - Central Division Club - K9ZC
>
>Email: bill@wjschmidt.com
>WebPage: www.wjschmidt.com
>
>"If computers get too powerful, we can organize them into a committee;
>that
>will do them in." -- Bradley's Bromide
>
>
>----- Original Message -----
>From: "Carcia, Francis A HS" <francis.carcia@hs.utc.com>
>To: "Amps (E-mail)" <amps@contesting.com>
>Sent: Thursday, March 31, 2005 3:09 PM
>Subject: [Amps] Solid state amps
>
>
>> Hi all,
>> I've collected parts to do 9 push pull MRF150 stages and someday maybe I
>> will assemble. The boards will
>> be modified ENI surplus. I found ENI transformers don't work well below 7
>> MHz. and the typical type 43
>> sleeve doesn't work well below 3 MHz. I found it takes 2 sleeves in
>series
>> to get minimum primary inductance
>> on 160 meters. These are the .875 inch O.D. sleeves. I wonder if anyone
>> has
>> also noticed this on 160 M.
>> I have also seen this with CCI kits. I plan to run DC through the
>> transformer because I found it forces a better
>> balance with MRF429 bipolars. Frank, WA1GFZ
>>
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>
>
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Best,
Will
Amateur Transformer & Supply
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