[Amps] plate choke

[Will Matney]

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

On 8/26/05 at 3:41 AM R.Measures wrote:

>On Aug 25, 2005, at 9:33 PM, 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.
>
>A single-layer choke of up to c. 60uH will exhibit no resonances below 
>approximately 35MHz, however, larger chokes will.


Not in the normal ham bands I doubt it. I have seen them though, well lets say in other places close. However a choke for that frequency needed to be used. It was around 22 uH so that should give a hint.

>
>>  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.
>
>Choke fires are definitely not an old wives' tale.  To avoid burning 
>one's hair, choke resonances need to be parked with care

Amen! That reminds me of the problems in some of the old Henry amps where the top few turns went POOF!


>>
>> 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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>>
>
>Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
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Best,

Will