[Amps] Parasitics & Filament Sag

[Steve Thompson]

R L Measures wrote:
> 
> On Aug 30, 2006, at 1:17 PM, Steve Thompson wrote:
> 
>>
>>>>> Any change in current causes a resonant circuit to ring. Ringing
>>>>> amplitude depends on how fast the current changes and on Q.    Faster
>>>>> and
>>>>> more Q =s more V.  I have heard from more than a few TL-922    
>>>>> owners who
>>>>> report that a big-bang, flashover, and damage occurred  when  
>>>>> their  922
>>>>> was un-keyed.
>>>>
>>>>
>>>> Sure, but how fast does the current change? By the time the  decoupling
>>>> capacitors have charged to allow the tube to drift into cutoff,  I  
>>>> doubt
>>>> the rise time alone is going to make the anode ciruit ring at vhf.
>>>
>>>
>>>
>>> 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.

Steve