[AMPS] Re: [super cathode]

[Rich Measures]

>
>hi all,
>
>> 'Super cathode driven' applies to a tetrode where the
>> screen is grounded and the grid is operated at 0 RF-V
>> with respect to the cathode.  Thus, there is never any
>> grid current in a super cathode driven amplifier
>> circuit. 
>
>not necessarily.  'super cathode driven' is where a fraction, call it  "k"
>of the driving potential applied to the cathode  is applied to the grid 
>as well, thus providing some negative feedback.  if "k" is zero, we have 
>normal cathode-driven operation (i.e. the grid doesn't move, the cathode goes
>up and down.)  if "k" is unity, the grid chases the cathode up and
>down, tracking it exactly. 
If K is unity, the grid is tied to the cathode.  Tying the grid to the 
cathode seems unlikely to produce amplification unless a (grounded) 
screen is present.  
> it is *definitely* true, however, that the 
>most reasonable thing to do when using this mode with a 
>tetrode is to make "k" equal to unity, i.e. the grid and cathode are 
>at the same rf potential, and therefore there is no chance of the 
>control grid drawing any current (assuming the tube is biased at a 
>reasonable operating point.)
If the grid and cathode are at the same potential, the grid can not draw 
current even if the tube is biased at an UNreasonable operating point.  
>just picking nits....
>
>73,
> 
>George T. Daughters, K6GT

Rich---

R. L. Measures, 805-386-3734, AG6K   


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