[Amps] AMPS

[Joe Subich, W4TV]

Measures writes: 
 
> If the anode potential fell to a very low level during parasitic  
> regeneration, electrons from the 3, 8874s' cathodes would mostly 
> flow into their grids, causing a >18A burst of grid-current which 
> would quite likely cause the 5A-rated Q1 to C-E short.  .

Anode potential falls to a very low level without corresponding high 
anode current?  Amazing but not possible.  The plate current pulse 
would cause the control board to take the HV off line and quench 
any activity. 

In any case, VDR1 shown between the cathode and chassis would likely 
short if the cathode flew high enough to support your claimed 18 A 
grid current pulse.   

> > Once again, fast electronic protection takes the amplifier 
> > off-line. I repeat: Q1 is a bias transistor, it is NOT part 
> > of the protection circuit, and it is NOT required to interrupt 
> > large currents.
> 
> Even during a VHF parasitic?

Yes .. yes ... and yes again.  The power for the parasitic has to 
come from somewhere.  The parasitic must also generate an anode 
current pulse to "feed" itself - properly designed safety circuits 
will remove both HV and drive (and generally open the cathode as 
well) when high grid and anode currents are sensed at the same time. 


73, 

   ... Joe, W4TV