I did not say that RCA recommended the G2DAF circuit. What I did say was
that RCA published and recommended a circuit where the screen was not
regulated. It simply means that a blanket statement that states that an
amplifier cannot be linear unless the screen is stabilized is wrong, and
that if that is the justification to prove that a G2DAF circuit will not
work, then it is ignorant.
Eimac states that a 4CX1000 being grid driven with absolutely stable screen
voltage has 3rd order distortion products of -23 db. That does not prove
that regulating screen voltage is bad, nor that the whole idea is nuts. The
same circuit using a 4CX1500 results in something like -44 db 3rd order
distortion.
To argue that the G2DAF circuit is bad because one example, with unknown
screen voltage time constants, was distorted and "because the screen voltage
must be regulated and therefore if it is not regulated it has to be bad" is
not a sufficient argument to convince me that I should reject the G2DAF
circuit.
The theorem that the G2DAF has to be bad because it has varying screen
voltage must be questioned. If indeed this circuit is so bad, then it would
seem that if the screen voltage varies from zero to hundreds of volts during
modulation, the 3rd order distortion products would be more than -22 db.
And, if the amplifier you heard was using a 4CX1000 tube, then it would be
within 5% of meeting the specs published by Eimac. So, if you listened to a
G2DAF amp without feedback and determined the distortion was -22 db, then it
is possible that you would have heard -22 db distortion if the amplifier
screen was regulated to .0000000000001%.
Colin K7FM
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