[Amps] Parasitics & Filament Sag

[Steve Thompson]

> Mistuning apparently does not cause instability.  The circuitry that  
> generates the VHF signal that starts the oscillation comes before the  
> tank circuit.  This source is the series resonant circuit that  
> consists of the anode-C's X (reactance) to gnd, the anode-lead's X,  
> the VHF suppressor's X, the DC-blocker's X, and C-Tune's XC to gnd.   
> Since the X of the anode-C is many times higher than the X of C-Tune,  
> adjusting C-Tune from max to min typically changes the resonant freq.  
> only a few %. Whenever anode current changes quickly, said resonant  
> circuit rings and generates a damped wave signal.
What rise/fall time is needed to start something ringing at (say) 120MHz?

Steve