[Amps] Re: Amps Digest, Vol 12, Issue 59

[R.Measures]

>> **  The grid does not and can not draw current when a competent
>>operator........
>
>Oh yes it can....! If you can show me a transceiver with an ALC loop which
>doesn't transiently produce output spikes significantly in excess of the
>steady-state level, then I'd be prepared to believe that control theory is a
>form of magic.

**  All transceivers overshoot.   A competent operator knows to  Not  
tune up a Class AB1 amplifier for SSB use with AØ/NØN/"hammer-down" 
because the  peak output V will not be developed from the driver with 
AØ... .   Instead, he/she uses a tuning pulser so that the true peak 
output potential  is fed to the grid.  Thus, when the DC  grid bias 
potential is subsequently set for zero grid-I, there will be none during 
actual operation.  
>
>A competent operator can certainly set-up the output of a transceiver to
>keep out of indicated grid current in the steady state, but in the real
>world with typical ssb transmitters, that's a highly simplistic view.
>
**  Competent operators do not have a simplistic view.  They know that 
the DC grid bias potential needs to be set so that there is no 
grid-current under maximal peak (not AØ) drive conditions.  Once the grid 
is set for 0-current, if needed, the ZSAC can be tweaked with the 
screen-V adjustment.  However, this process is simpler if a transceiver 
with front-panel power-adjust is being used.  

>For excellent linearity, a tetrode linear amplifier of any size really does
>need stable, low impedance supplies for G1 and G2. 

**  For G2 in Class AB1, undoubtedly.  For G2 and G1 in Class AB2, yea 
verily, but not for G1 in AB1.  

>It doesn't need a higher
>degree in thermionic electronics to understand why. In a class-AB1 tube
>amplifier, the dc currents flowing in both the G1 and G2 circuits are
>powerful diagnostic tools, providing the supply voltages are stable.
>
**  There is no more than Zero DC G1 current in a thermionic Class AB1 
amplifier.

>Just because Collins used a number of short-cuts in their transmitter
>designs of the the '50s and '60s, it doesn't necessarily mean that we should
>follow their practices slavishly half a century on. It's now possible to
>make good G1 and G2 power supplies for a few tens of euros/dollars, and
>these have effctively obsoleted earlier practice.
>...
>Chris