[Amps] Plate choke magic?

[wc6w at juno.com]

Hi Tomm,
  A powdered iron part will still need quite a few turns.

  For instance:  70 turns on a T-200A-2 will provide 100uH.  This should be a rough equivalent to the commonly used value.  Try it?

  Check for resonances in an installation & then measure how warm it gets at 3.5 MHz -- The air core chokes only have wire losses down there.  This approach will also have some core loss.  

73 & Good morning,
  Marv  WC6W


-- Tomm Aldridge <KD7QAE at ARRL.NET> wrote:
Marv,
Thanks for the references, I will read them.  To be clear, I was not 
proposing ferrite toroids but powdered iron toroids as they can support 
DC due to their distributed gaps.
Tomm

wc6w at juno.com wrote:
> 
> 
>>-- Tomm Aldridge <KD7QAE at ARRL.NET> wrote:
>>Why are plate chokes seemingly black magic?  Don't you just want a >good decoupling of the PS from the Plate; i.e. lots of impedance from >DC to Light and no resonances?  How I get that should not be an issue >but all teh plate chokes I see are long skinny and sometimes segmented >single layer solenoids of questionable wire size.  Why wouldn't a >really lossy powdered metal toroid with a few fat turns on it work, >assuming the inductance was high enough?
>>
>>KD7QAE
> 
> amps at contesting.com
> 
> Hi Todd,
>   No magic involved.
> 
>   A compromise was reached long ago that most ham amplifiers have employed ever since.  By allowing the plate choke to carry some reactive current at its lowest frequency of operation, the value may be reduced such that only a single series resonance occurs within the 3-30 MHz region, which may then be conveniently placed at a "safe" frequency.
> 
>   The long form factor provides the best L/C(stray) ratio. 
> 
>   This topic is well covered in: "R.F. Chokes for High Power Parallel Feed",  by Vernon Chambers, QST, May 1954, pp30-33.
> 
>   A toroid would not be the best choice for a ferrite loaded plate choke due to the large DC component which would tend to saturate a closed magnetic circuit.
> 
>   A reference on this approach is: "A Unique RF Plate Choke", by Bill Deane, 73, Sept. 1969 p. 147.
> 
> 73 & Good afternoon,
>   Marv WC6W
> 
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