>>>Is the tube better in grounded grid configuration as I see
>>>most 4-1000A schematics, or is it better in grid driven configuration?
>>>
>>How better? The answer is not yes or no. Efficiency is a bit higher in
>>AB2 cathode-driven, however, the drive requirement is higher than for AB1
>>grid-driven. For wide freq. coverage, the tuned input circuit for
>>grid-driven is less complex than for a cathode-driven amplifier.
>
>Well, since the efficiency of a tube PA ain't real good anyhow, big deal
>from what I can tell. The fact that drive power is less and that the
>tuned input is less complex seems to outweigh the efficiency side. How
>much higher is a "bit higher."
>>
Depends on the anode and screen supply potentials. In grid-driven
service, the minimum anode potential during peak drive is no less than
the screen potential, which in this case is 1000v. However, in cathode
driven service, the min. anode potential is typically 300v. -- in other
words, the anode headroom is roughly 700v wider in cathode-driven
service.
>>>I know that grid driven will give me more gain, but how much more?
>>
>>Roughly double for a one-tube amplifier. Roughly quadruple for two-tubes
>>in parallel.
>
>So going from 12 dB gain to 24 dB gain is a BIG deal. To me having more
>available gain would mean that in order to drive the tube to legal limit,
>it does not have to be driven so hard.
Similar peak anode current would be needed to produce 1500w output for
either grid-driven or cathode-driven.
>........
>>Neutralization in AB1 is only for the fundamental frequency, not for the
>>VHF anode resonance. It is my opinion that VHF oscillation is similarly
>>problematic in either config.
>
>Well, I'd agree. However, with more gain at all frequencies, your gain
>and phase margins have shifted a bit and that is what concerns me. But
>perhaps it's not that bad.
With neutralization, there is zero feedback at the operating frequency.
>
>Interesting stuff to think about.
>
>Thanks Rich.
>
ur welcome, Jon
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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