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@outlook.com>
To: "Amps" <amps@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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