[AMPS] Zener screen supplies

[Tom Rauch]

> >Actually, the MOV is a last resort just to protect the socket 
> >capacitor...as would be a gas tube. 
> 
> The MOV or gas tube at the screen terminal is actually the *first*
> line of defense because that is where the arc hits. Tom correctly
> identifies that the screen bypass capacitor in the socket is at least
> as valuable and important as the tube. The tube may survive, but if
> you blow that capacitor, you need a whole new socket.

It is last because the voltage is too high for it to be "first". Hopefully 
it is last, and not the socket!
 
> However, slowing the transient down - stretching and lowering it -
> requires some kind of series impedance. This is where it gets tricky,
> because in most designs the series impedance will tend to spoil the
> voltage regulation in normal operation.

Ian, the impedance is normally in the anode. 
 
> >That's a good idea with almost any regulator. I can't imagine NOT
> >using one!
> 
> One word of caution. Don't connect the electrolytic directly in
> parallel with the screen bypass capacitor. The self-inductance of the
> electrolytic will parallel-resonate with the bypass capacitance,

I doubt that will happen with any large impedance peak because 
the RF Q of the electrolytic so low, but if it does they make ferrite 
beads.
73, Tom W8JI
W8JI@contesting.com 

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