William,
That's what I thought you meant but wasn't sure. Yup, that would work fine as
your killing the DC component from the transformer. I've seen this design used
in a few places. I dont know why it isn't used more unless they're too tight to
add the chokes and blocking caps. Really. all you need for the choke is another
transformer core and can be smaller than the RF output one. You use the center
tap for the DC feed and hook each end to each collector behind C block. I think
Helge used that on some designs with and without the C block. This core was
about 1/2 the size or smaller of the RF output one if I recall. Actually, I
think they used preformed balun cores which are molded as one piece and have
two holes through them. The RF output was made either by stacking toroids or
using longer sleeves about 1-1/2 to 2 inches long. They were 1/2" O.D. and
9/32" I.D.. Helge used #43 material, but the core manufacturers told me I
should use #61 for 2-30 MHz.
Best,
Will
Amateur Transformer & Supply
*********** REPLY SEPARATOR ***********
On 3/31/05 at 10:55 PM Dr. William J. Schmidt, II wrote:
><<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? >>
>
>Yeah that's what it means...you got it... the collectors are fed via a
>choke
>that is bifilar wound with a center tap for the DC+, while the RF
>transformer is cap coupled (DC blocked). Check Helge Granberg's later
>designs... they were all done this way because he recognized the problem.
>
>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: "Will Matney" <craxd1@ezwv.com>
>To: <amps@contesting.com>
>Sent: Thursday, March 31, 2005 10:46 PM
>Subject: Re: [Amps] Solid state amps
>
>
>> 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
>>>>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>
>>>
>>>_______________________________________________
>>>Amps mailing list
>>>Amps@contesting.com
>>>http://lists.contesting.com/mailman/listinfo/amps
>>
>> Best,
>>
>> Will
>>
>> Amateur Transformer & Supply
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
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