Still, I think you are definitely on the right tract. Forgoing a feedback loop is worth pursuing in its own right. My own twist would be to add a switch that would allow switching the output stage on or off, so that I could double the usefulness of the power amplifier by including a 6 pin jack for electrostatic headphones.
A good test bench for this idea is the Dynaco ST-70, as the 6SL7 and 6SN7 could fill the two front 8 pin sockets and two 6550s could fill in the two back sockets. True, this would render the stereo amplifier a mono block amplifier, but the power supply was somewhat overly tasked before anyway; now, it would loaf. The negative power supply rail could be derived from completing a full-wave bridge center-tapped circuit by adding to solid-state diodes and one high voltage capacitor to the power supply. This arrangement would still allow for using the GZ34 rectifier tube.
Subject: Great webzine...
I just found your webzine, and really enjoyed it. It must be really a labour of love. It is, as you say, very rare to find anyone looked behind the hype and claims at the theory and electronics of tube amplification. This is what interests me (along with listening to music of course). A few comments...
I have a pair of M60s, by now very heavily modified, and have followed numerous arguments about whether they are really class A, their output impedance, and so on. Sometimes I contribute (mainly on the owners group) but I have got tired of being flamed when I do so. The truth is that they have an output impedance of around 11 ohms, and they cannot possibly be Class A all the way. They have a meaningful power output of around 25W into 8 ohms. Also they never go into A2, because the 6SN7 driver circuit cannot provide the huge currents involved. Most importantly, they sound absolutely wonderful, with a