[Amps] Parasitics & Filament Sag

[Steve Thompson]

R L Measures wrote:
> 
> 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 hope not, I looked from 1MHz up to around 300MHz, in both full and 
part band sweeps. Around the tuned frequency was the only place I found 
repeatable signals. It's a laborious process as a spectrum analyser (at 
least the ones I have) is unsuited to catching a short duration signal.

Steve