Either of them (And other amplifier builders who have similar view) are far more qualified than me to debate this point with you. I can say that their comments make plenty of sense and are backed up by their SET amplifier performance results. I just listen and read in an attempt to learn.
@charles1dad
What they are doing is a brute force thing by running lots of current through the tube so they can have lots of current drive on the grid.
Of course by simply paralleling elements in the 6SN7 they could do the same thing... but at any rate, there is a series impedance (the coupling cap) which limits how much current can be delivered to the power tube grid. So they are going for overkill.
But if you direct couple you solve this problem, although to do it effectively you have to run the driver tube with no voltage gain. That’s exactly how we’ve done it in our OTLs. The advantage of this approach is there is no overload recovery time- its instantaneous as there are no timing constants present between the driver and power tube grid. But it does make for what appears to be a more complex circuit, something that seems anathema to SET designers.
However, there is another advantage: the coupling cap that you do have to have to couple the signal to the driver tube can be a considerably lower value, usually by at least an order of magnitude, possibly more. This means that no matter what the coupling cap, the smaller cap will always sound better. So you have a double whammy.
The downside is the driver tube isn’t available for gain. But that’s OK- being a lower powered amp, an SET doesn’t need much gain (certainly less than we have in our OTLs).
The funny thing is you could execute this with the same number of tube sections as used in a traditional SET right now (three total, including the power tube). The reason you don’t see this is the fact that you have to build a negative power supply. But if you did, you could build an SET that was inherently lower distortion which means it would be more transparent.
