HighDeaf1080p wrote:How do I measure what load the boost stage is inflicting on the 5088, in comparison to the 100k pot?
You could measure current through P5 and watch the collector voltage to determine of that transistor is working as hard.
In my mind, an easier method would be to temporarily short C5 and measure DC resistance from the collector of the 2N5088 to ground. That is your load, as filtered through C5 (which introduces a variable in terms of bandwidth, but let's not complicate things...). Executing a similar test with the BS170 circuit will illustrate that the load on the 2N5088 is lifted by the very high input impedance of the FET and the zener (which is in a position I have never used personally, so once again I'm going to point out that I don't have any knowledge of what's going on there).
To further complicate things, in the original version you also have whatever input stage of the following device electrically adding to the load that the 2N5088 sees as it is in parallel with the output pot (between common and wiper), but this is a very, very minor element in comparison to the changes you've implemented.
tl;dr: slapping a 100K resistance to ground with DC blocking (a cap) between the two actives there would be my initial thoughts on exploratory surgery.
Furthermore, if the DC potential between the collector of the 2N5088 and the gate of the BS170 is similar I'd bypass C5 to see what happens (putting C5 in series with the aforementioned 100K load).