[Amps] Parasitics & Filament Sag

[Tom W8JI]

>> 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.

That can be because of relay sequencing. Known to be a 
problem in the stock TL922.

> 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.

Because of bypass caps and other component values, the 
ringing can never have a higher peak at VHF than it has at 
HF.

73,
Tom