4. Which circuit to use?
Additional design objectives for the gain stages are a low output impedance and a good power supply rejection ratio (PSRR) figure. A quick survey of possible circuits reveals that the need for a low Zo precludes the use of the Cascode amplifier and, to a lesser extent, the Grounded Cathode amplifier. This leaves the Totem-Pole and the Constant Current Draw Grounded Cathode (CCDGC) amplifiers as the best candidates. The Totem-Pole offers a better PSRR figure and a single current path; the CCDGC, a constant power supply current draw and a lower Zo. Because the Totem-Pole requires an internal coupling capacitor, which can prove both expensive and complicated to bias, the CCDGC amplifier wins in this example. Where expense is not an issue or limited current sourcing from the power supply is an issue, the Totem-Pole wins. The CCDGC amplifier consists of a Grounded Cathode amplifier directly cascaded into a Cathode Follower. Each triode sees the same cathode to plate voltage and the same load resistance and current draw. Both are in voltage phase, but not current phase. (As the grounded Cathode amplifier sees a positive going input signal, its plate current increases, which increases the voltage developed across the plate resistor, which in turn swings the plate voltage down. This downward swing is then cascaded into the grid of the Cathode Follower, which decreases the plate current to the same degree that the previous stage's current increased.) This results in the constant current draw feature of this topology (a highly desirable feature, as the signal amplification will not alter the amount of current being sourced from the power supply and consequently not perturb the power supply, thus greatly simplifying the design consideration of the power supply).

5. Which tube to use for the first stage?
Very few tubes stand out as being exceptionally quiet. The 6DJ8 and the 12AX7 come first to mind. If tube microphonics are ignored, then the 6DJ8 wins, as its six-fold greater transconductance results in a much lower internal resistance noise (and in a much lower output impedance) than the 12AX7. However, many 6DJ8's are quite microphonic, which means some hand picking of tubes will be needed for the critical first stage 6DJ8.  (The current darling of the tube audio underground press, the WE 417, is usually horrendously microphonic.)

6. How much plate voltage and current to use?
The 6DJ8 type tube has one of the lowest published maximum cathode to plate ratings of the 9 pin miniature tubes (the actual maximum cathode-to-plate voltage might be much greater, if anyone has any intelligence on this value, please send to us). On the other hand, it can sustain a good amount of plate current, although the published 15 ma is a bit too optimistic. Good starting points would be a healthy (but sane) cathode to plate voltage of 100 volts and somewhat heavy current draw of 10 ma per triode.