On Oct 1, 2005, at 7:04 AM, Steve Thompson wrote:
> R.Measures wrote:
>> On Oct 1, 2005, at 3:59 AM, almacottage wrote:
>>
>>
>>> i have the AL811 with 3 tubes , i directly swapped the 811a tubes
>>> for
>>> 572B tubes and run the high voltage at 1900v [ie in the red segment
>>> of
>>> HT meter] .
>>>
>>> i found that on these amps the original anode parasitic chokes
>>
>>
>> In a HF/MF amplifier, R//L VHF parasitic suppressors are not
>> "chokes".
>> They are a device that reduces the VHF Rp* presented to the anode.
>> Less Rp means less VHF amplification, which in turn means more
>> stability at the anode's unavoidable parasitic resonance. (typically
>> from 43MHz to 160MHz)
>>
>> * Rp = Parallel-equivalent R. Achieving less VHF Rp requires less
>> VHF
>> suppressor Q.
> Also, don't forget that the Rp seen by the tube is the Rs (series
> equivalent resistance) of the suppressor network at the vhf frequency
> in
> question.
>
True, Steve. The amplification formulas for Rp and Rs are different
but they give the same result.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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