Tom,
I should have added earlier that if the choke will work at the lowest
frequency, it will on every other higher frequency, providing it isn't resonant
at one of them. In other words, you design the choke for the lowest frequency
it will handle. When measuring for the coils self resonant frequency, find the
dip with a grid dip meter and use a frequency counter coupled with the meter to
see what the actual resonant frequency is. Just a few turns +/- will move the
self resonant frequency a good bit. That is what's known as "parking" the
resonant frequency elsewhere. Just make sure it's "parked" where a
non-operating frequency is.
Best,
Will
*********** REPLY SEPARATOR ***********
On 8/25/05 at 9:52 AM Will Matney wrote:
>Tom,
>
>All you have to do is make sure it's not resonant on one of the operating
>bands. If it is, you can park that frequency somewhere else by adding or
>subtracting a few turns of wire. To check its resonant frequency, short
>the coil with a jumper, then use a grid dip meter to measure it. The main
>thing is that the choke has to have enough inductance at the lowest
>frequency to block the RF.
>
>Best,
>
>Will
>
>
>*********** REPLY SEPARATOR ***********
>
>On 8/25/05 at 2:44 PM KD7QAE wrote:
>
>>So, Are you telling me that at every operating frequency of the amp I
>>have to design the plate choke so that it has a parallel resonance?
>>That is impossible without adding some sort of tuning mechanism, which
>>clearly isn't done in practice. You cannot count on parallel resonance
>>for the general wide band plate choke design. I agree w/ Rich's analysis.
>>
>>Tomm, KD7QAE
>>
>>R.Measures wrote:
>>
>>>On Aug 25, 2005, at 4:52 AM, Roy Koeppe wrote:
>>>
>>>
>>>
>>>>If...
>>>>
>>>>"Reactance at 1.8MHz = 3099 Ohms"
>>>>
>>>>Then,
>>>>
>>>>With 3 kv on the plates, circulating current through the choke winding
>>>>and through the by pass cap is 1 amp?
>>>>
>>>>
>>>
>>>With a 3kV anode supply, The peak change in anode potential is c.
>>>2700v-pk 0.707 x 2700v = c. 1900V-rms, so the circulating current
>>>through the HV-RFC is 1900v / 3099-ohms = 0.616A-rms
>>>
>>>
>>>>You see, this is a useless parameter.
>>>>
>>>>
>>>
>>>Not quite since the HV bypass C must be able to carry 0.616A at 1.8MHz
>>>without overheating and igniting.
>>>
>>>
>>>
>>>>Circulating current is limited by
>>>>parallel resonances in the winding,
>>>>
>>>>
>>>
>>>At 1.8MHz, with a typical Ham amplifier - I don't think so.
>>>
>>>
>>>
>>>>which present a much higher
>>>>effective resistance to the tank circuit.
>>>>
>>>>73, Roy K6XK
>>>>
>>>>_______________________________________________
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>>>>
>>>>
>>>>
>>>>
>>>
>>>Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>>>
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>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>>
>>>
>>
>>
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>
>
>
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