I'm playing around with an optimization to the circuit and was wondering if I could post a survey question. All the measurements I'm asking for are available via the test points, so it should be easy
voltage to ground from each of the battery test points
voltage to ground from each of the outputs to ground
I remember seeing a few of the folks not be able to get the output to ground measurement to zero, which impacts the maximum swing on the amplifier. For example, Inu's build. I think I might see the problem here (a small problem, granted 50V here isn't a huge deal, but for us that are perfectionists...), which is due to the fixed base biasing method of the darlington servo pair. Thus the hfe of the transistors might very likely have been hand-selected by Stax with a certain beta that has been lost to posterity. Also, the fact that the original was a furnace would have an impact on this aspect of the circuit.
For extra credit, I'd love at least one person who can zero things out to measure voltage across R73 (6.2K) and R64 (510R) for one channel (I can send beer as a thank you!)