[Amps] Passive grid stability calculation for a tetrode?

[peter chadwick]

For 10kW PEP out, 600 volts peak to peak on the grid in AB1. At 30 MHz, that's 4.7 Amps of RF into the input capacity!

73

Peter G3RZP


========================================
 Message Received: Nov 15 2013, 02:44 PM
 From: donroden at hiwaay.net
 To: "Amps" <amps at contesting.com>
 Cc: 
 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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