Ralph has written in the past that the 6SN7 is a sufficient driver tube “dependent “ on its implementation in a given circuit. I have been told that the 6EM7 provides much more current, power and drive capability compared with the 6SN7.
I will say that I’ve heard an excellent sounding PSET 845 amplifier that utilized the 6SN7. I could certainly be wrong, but isn’t the 845 a more difficult tube to drive than the 300b?
@charles1dad The issue is always how much voltage swing will drive the tube to full output and how much grid capacitance is there. The more grid capacitance, the harder the tube is to drive.
You can get a 6SN7 to drive a single 300b no sweat. But doing it the way is traditionally done in SETs will likely but the tube at a disadvantage.
The 6EM7 does have one section that is considerably more gutsy than a 6SN7 has. But you will always be looking on the collector's market for replacements.
The way to get a 6SN7 to really do the job is to have it wired as a cathode follower direct-coupled to the grid of the power tube. In this way the coupling cap used in the amp stays rather small since its driving the 6SN7 rather than the output tube. Smaller caps are more transparent...
This is the technique we've used in our OTLs for several decades now. Its very reliable. One 6SN7 section is thus able to drive a number of highly capacitive triode grids with the voltage swing needed. I do not understand why this approach hasn't been used in SETs since the design consideration is similar. It might be because a negative power supply would be needed. But from what I've seen, SET users are not particularly worried about cost if the amp gets the job done for them.