[Amps] Passive grid stability calculation for a tetrode?

[Carl]

Even CBers can build stable grid driven 4X5's!  It is a very hard tube to 
make oscillate.

The SK300A socket requires good screen bypassing for RF.

Carl
KM1H


----- Original Message ----- 
From: "peter chadwick" <g8on at fsmail.net>
To: "Markku Oksanen" <ww1c at outlook.com>; "Amps" <amps at contesting.com>
Sent: Friday, November 15, 2013 5:44 AM
Subject: Re: [Amps] Passive grid stability calculation for a tetrode?


> 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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