[Amps] Parasitics & Filament Sag

[R L Measures]

On Sep 1, 2006, at 3:25 AM, Steve Thompson wrote:

>
>>>>>> During the Grate Parasitics Debate in 1996, a member of the   
>>>>>> audience
>>>>>> hauled his SB-220 to work and loosely coupled the anodes to a HP
>>>>>> spectrum analyzer.  When the 220 was keyed, he observed damped- 
>>>>>> wave
>>>>>> ringing at 112MHz at on And at off.
>>>>>
>>>>>
>>>>> I wish I could reproduce that. I've tried repeatedly with spectrum
>>>>> analyser and 'scopes and only ever find operating frequency  
>>>>> ringing,
>>>>> even with suppressors removed.
>>>>
>>>>
>>>>
>>>> Apply no driving signal and rapidly key the T/R bias.
>>
>>
>>> Did that, no result. Hence my post.
>>
>>
>> ¿You found the driving signal, but you applied no driving signal?
>> Please describe the coupling method to the S.A.
> I should have said 'ringing close to frequency the amp was tuned to'.

You were looking in the wrong part of the spectrum.
>
> I tried various couplings - a few inches of wire into a high impedance
> fet probe poked in lots of places. 1pF directly from the anode into  
> the
> analyser via a 30dB pad. A two turn coil of wire 1.5" dia. placed
> everywhere I could physically get it.
>
> Steve
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R L MEASURES, AG6K. 805-386-3734
r at somis.org