> maximum gain is at minimum gm
Yes; but Gm only varies 7%. I think it is swings and roundabouts: as one factor changes, another changes, so the net change is small.
> K voltage as near as possible to 1.12V
Where does that magic number come from? Some assumed peak input voltage? (for 1:7? 1:10? 1:20 iron? For far-mike ribbon on harpsichord or dynamic on full orchestra?)
My thought is that Rg2 is not a primary parameter, Vg2 is. Rg2 is useful for self-bias because a hot cathode will suck more Ip and Ig2, the lower Vg2 means lower current, so tube interchange is improved (variability is less). Rp is not a primary parameter, as long as Vp lands in a flat spot of the plate curves and has some swing both ways. (Not a lot of swing because this will surely be followed by another stage; 10V swing is plenty.) And rp has not fallen so far as to reduce gain much.
To go too far afield: Vg1, Vg2, and gain are interrelated. Vg1 will tend to be near Vg2/Mu(g2), and gain will approach Vp/Vg1. For max gain, set Vg2 as low as possible for the required Ip(peak). For large power out (not needed here), set Vg2 higher. I have no idea where along this line might be lowest EIN.
Yes; but Gm only varies 7%. I think it is swings and roundabouts: as one factor changes, another changes, so the net change is small.
> K voltage as near as possible to 1.12V
Where does that magic number come from? Some assumed peak input voltage? (for 1:7? 1:10? 1:20 iron? For far-mike ribbon on harpsichord or dynamic on full orchestra?)
My thought is that Rg2 is not a primary parameter, Vg2 is. Rg2 is useful for self-bias because a hot cathode will suck more Ip and Ig2, the lower Vg2 means lower current, so tube interchange is improved (variability is less). Rp is not a primary parameter, as long as Vp lands in a flat spot of the plate curves and has some swing both ways. (Not a lot of swing because this will surely be followed by another stage; 10V swing is plenty.) And rp has not fallen so far as to reduce gain much.
To go too far afield: Vg1, Vg2, and gain are interrelated. Vg1 will tend to be near Vg2/Mu(g2), and gain will approach Vp/Vg1. For max gain, set Vg2 as low as possible for the required Ip(peak). For large power out (not needed here), set Vg2 higher. I have no idea where along this line might be lowest EIN.
