[Amps] Passive grid stability calculation for a tetrode?

[donroden at hiwaay.net]

How much grid voltage swing for AB1 ?
( how many watts into a 50 ohm load )

Don W4DNR


Quoting Carl <km1h at jeremy.mv.com>:

> 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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>
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