[Amps] Silly question - interim report on results.

[Peter Chadwick]

Tom said:
>Why?  Q of one small part of a complex system doesn't 
determine anything by itself. If it did, we'd never be able 
to build a R/C oscillator circuit now would we?<

But we have a case here where the Q of the whole grid circuit is much less than 1, i.e. it looks very resistive . At least over the frequency range I have  problems with - there's no VHF parasitic problem here.

Don't quite follow about the RC oscillator - they rely on successive phase shifts, rather than Q in the terms of energy stored over energy released. Same with a ring oscillator.
A quick calculation suggests that the feedback path loss (ratio of AC grid volts for a given AC plate volts) is -56dB, while the forward gain (ratio of AC grid volts to AC plate volts) is 34dB.

>Many of these resistor swamped grid driven PA's are hanging 
on the very edge of the instability zone. Look at the grid 
impedance, the anode impedance, and the feedback of the 
system.<
That's going to be especially so with some of the very high gm tubes, like the 4CX1000/4CX1500. It's also going to be very wasy to have effectively no (or very little) effective swamping resistance at VHF because of lead lengths.
But this damn thing is ONLY doing it on the top end of 80 metres - not on 7MHz or higher!
Maybe I need some nichrome....
73
Peter G3RZP