[Amps] AL-811H etc

[R.Measures]

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