[AMPS] 3CX300A1 for AB1 GG

[Rich Measures]

>
>Rich says:
>
>	>?  What is the Mu of the tube, Tom.  
>
>The data sheet doesn't give it. It does give ra and gm, from which I work
>out 
>mu = 9.
>
>I'll stick my neck out now:
>
>This is a very bad choice of tube for RF GG service. It is rated as an audio
>tube;it has four cathode pin connections and one grid pin connection, plus
>the centre spigot, so 'grounding' the grid correctly at higher frequencies
>will be difficult. It requires the grid to be floated at 100 volts or more
>negative to cathode; it has insufficient mu to be a good grounded grid
>stage, and insufficient grid dissipation capability to be run without some
>very good protection circuitry. ALC might save the grid, but will almost
>certainly lead to very bad intermodulation products, unless the grid supply
>is very 'stiff'. There are no RF ratings for this tube, and the absolute
>maximum plate voltage is 1800 volts. The listed 'output' capacity for
>grounded cathode (1pF) suggests that it could well have stability problems
>on the higher bands (21MHz and above)
>
>
>OK Rich, Tom, any comments?
>
You can't get an AB1 triode to turn on hard at zero grid-volts unless it 
has a Mu of more than 4 or so.  
AB1 triodes are problematic at frequencies over a few hundred kHz.  
>
-  later, Peter
>> ----------
>> From: 	Rich Measures[SMTP:measures@vc.net]
>> Sent: 	27 July 1999 23:22
>> To: 	W8JI@contesting.com; amps; ohashi
>> Subject: 	Re: [AMPS] 3CX300A1 for AB1 GG
>> 
>> 
>> 
>> 
>> >
>> >> You are right if no ALC is used.  My idea assumes 1-10 mA grid current
>> >> (yes, it is little bit AB2), but ALC reduces driving power from the
>> >> excitor, resulting total IMD is not so bad. Remember 6146 AB1 GC in
>> KWM-2,
>> >> same thing.
>> >
>> >First, ALC is not that fast. Most rigs can't even keep up with 
>> >themselves, let alone a loop from an external PA.
>> >
>> >Second, any grid current will perturb grid voltage unless the grid 
>> >comes from a supply with low esr and good dynamic regulation.
>> >
>> >Third, you are locked into cathode drive without complex circuitry. 
>> >
>> ?  What is the Mu of the tube, Tom.  
>> > 
>> >73, Tom W8JI
>> >w8ji@contesting.com
>> >
>> >--
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>> 
>> 
>> 
>> Rich...
>> 
>> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  
>> 
>> 
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>
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Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


--
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