[Amps] Passive grid stability calculation for a tetrode?

[Carl]

About 300V PEAK

Carl
KM1H


----- Original Message ----- 
From: <donroden at hiwaay.net>
To: "Amps" <amps at contesting.com>
Sent: Friday, November 15, 2013 9:44 AM
Subject: Re: [Amps] Passive grid stability calculation for a tetrode?


> 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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> 
> 
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