[Amps] plate choke

[Will Matney]

When those soldenoid chokes were designed, first they figured for enough impedance at the lowest frequency. That decided the amount of inductance. Next, a trial choke was wound. Then, they used a grid dip meter most likely to make sure where its SR was. If its SR shown on an operating frequency, they moved the SR by adding or subtracting a few turns. Then, it was checked again with the dip meter. When all was well, that was the design. You'll notice on several chokes that none are hardly an even number like say 20, 40, etc uH. My guess is that was because the SR would show up in the wrong place. Anyhow, any text I've ever read on the subject always recommend using the grid dip meter to check where the SR was. The cure was always add or subtract a few turns.

There have been mis-designed chokes used before too! I have heard of some in some Henry amps where the few top turns would burn out. That was over SR and was cured by subtracting a few turns off the old choke.

Best,

Will


*********** REPLY SEPARATOR  ***********

On 8/26/05 at 5:33 AM KD7QAE wrote:

>So,  many of the plate chokes I have seen described in home brew 
>amplifiers and those in use in Ameritron, Henry, Alpha and QRO are 
>single layer wound solenoids, many like the one I built.  These do not 
>exhibit resonant peaks (High Z) in the ham bands as far as I can tell 
>based on my limited experience.  I am very confused by the assertions 
>that I need to build something materially different than these examples 
>or face a very inefficient and perhaps flaming amplifier.
>
>Michael Tope wrote:
>
>>----- Original Message ----- 
>>From: "Jim Forsyth" <jim at forsyth.net>
>>
>>  
>>
>>>This mini thread is about a case where the resistance of the inductor WAS
>>>significant and possibly DID affect the resonant frequency appreciably.
>>>
>>>Jim, AF6O
>>>
>>>    
>>>
>>>>At the risk of sticking my foot in my mouth again, R generally
>>>>doesn't effect the resonant frequency of an RLC circuit appreciably
>>>>provided that the Q is reasonably high. On the other hand, a plate
>>>>choke when you look at it very closely is really a distributed RLC
>>>>circuit, so one has to be careful about applying simplified 3 component
>>>>lumped element models. I'd love to see a rigorous analytical treatment
>>>>of this if anyone knows of a good reference.
>>>>
>>>>73 de Mike, W4EF........................................
>>>>      
>>>>
>>
>>Yes, I understand that, Jim, but I was having a hard time believing that
>>you could get away with deQing a choke enough to shift the resonant
>>frequency significantly without turning it into a fireworks display. I did
>>some google searching and there seems to be little in the way of
>>analytical information on plate choke design. Mostly it seems to be
>>an empirical art (e.g. use X # of turns closewound on a D diameter
>>form kind of thing). My best guess of the equivalent circuit would be
>>a bunch parallel RLCs in series, but even that I suspect is
>oversimplified.
>>The fact that it has multiple staggered parallel and series resonances,
>>for instance, can't be explained by a simple 3 component lumped RLC
>>model.
>>
>>73 de Mike, W4EF.............................................. 
>>
>>
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>
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