Christian bravo pour le projets. Wonderful to see a Tektronix afficanado, who appreciates curve tracers.
I did similar 577, 576 test adapters in 1980s, using two pieces of lucite 1/4" and hand wiring the Bannana plugs.....TO-3, TO-66, TO-220 and TO-247(?) also, power diode, and a very useful binding post adapter. But I didn't have your tube socket idea.
The Kelvin connection four terminal is critical for high current tests, 2 terminal will give substantial errors in the voltage at the contacts points. The two terminal limits are perhaps one amp. 576 with 177 pulsed test fixture has 1000A peak capability!
Note...The 576 and 577 plastic safety test fixture cover is easy to damage and a problem in testing large power devices or with long leads. I modified my 576 with an interlock "cheater" switch..DANGER DO NOT DO THIS... At the time I was designing and manufacturing 12 kw arc lamp power with 55 kV ignitors, so the 576 voltage was not worrying!
The 576 is still in mint condition, I got the original manuals, 177 pulsed current and SCR turn-off time adapter.
Keep up the fine work. Just the ramblings of an old retired EE