This is probably most relevent to the New First Watt product at Axpona 2023 thread: https://www.diyaudio.com/community/threads/new-first-watt-product-at-axpona-2023.398259/post-7325220I think it would be case dependent. I guess I would consider 12 dB near the boundary.
I went back to the FrankenTracer data for 6 of my 2SK182ES SITs. Several years ago I put together some GNU Octave (pseudo Matlab) code to fit 2D polynomial surfaces Vgs(Vds,Id) to that data. From those surfaces it is easy to compute mu, gm, and Rd for a given operating point.
Here as a few examples:
SIT#1 Vds=30V Id=1.5A mu = 16.984 gm = 6.7570 Rd = 2.5135
SIT#2 Vds=30V Id=1.5A mu = 17.186 gm = 5.8923 Rd = 2.9166
SIT#3 Vds=30V Id=1.5A mu = 21.176 gm = 7.2821 Rd = 2.9080
SIT#4 Vds=30V Id=1.5A mu = 19.416 gm = 5.9390 Rd = 3.2691
SIT#5 Vds=30V Id=1.5A mu = 20.880 gm = 6.0735 Rd = 3.4379
SIT#6 Vds=30V Id=1.5A mu = 20.540 gm = 6.9906 Rd = 2.9383
Below are images of the Vgs surface for SIT#4. The black line is a 16 Ohm load, corresponding to the load seen by the SIT when the mu follower and the SIT have equal, but opposite, AC currents.
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