[Amps] Passive grid stability calculation for a tetrode?

[peter chadwick]

Markku,

It may be shown that (i.e. as the books say, it is left as an exercise for the reader!) if you have H<2 as a result of solving the equation  H=gwCpgRpRg  where g is the mutual conductance, w = 2 times pi times frequency, Cpg is the pate - grid capacitance, Rp is the plate load resistance and Rg is the grid resistance, the stage is stable. Arguably Rp should be the plate load resistance in parallel with AC plate resistance of the tube, but sticking to the load resistance gives a bit more stability.

vy 73


Peter G3RZP


========================================
 Message Received: Nov 15 2013, 07:32 AM
 From: "Markku Oksanen" <ww1c at outlook.com>
 To: "Amps" <amps at contesting.com>
 Cc: 
 Subject: [Amps] Passive grid stability calculation for a tetrode?
 
 All
 I am back on my 4CX5000 project and as it not done yet, I am still contemplating the circuit to be used.Earlier this year I got solid info from this reflector for GG operation and that look like a pretty good solution.However, I was wondering about passive grid, grid driven also.
 The question is:  How do a calculate the stability?  If I simply do math for tube voltage gain I get something like 25.Then if I calculate the feedback capacitive voltage divider, Grid to Cathode 120 pf, Plate to Grid 0.7 pf, I get less than 0.01 for the ratio. If the beast needs the voltage gain times feedback gain to be above 1 to oscillate, to me it seems this tube is stable no matter what.  Where did I err if I did?
 Thanks!
 MarkkuWW1C 		 	   		  
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