Red Anode GU80 test

Our friend Zygmunt Jerzyński returns in full power with the new article in his outer scape elaborated way. Red Anode GU80 test article invites in full red vibrancy.  
I’m still alive, folks !
I tried not to exceed the maximum spec limits, and almost succeeded ..
Started easy and gentle …
But after that cranked it up to the full spec limit of the tube.
I stopped the long term stress test at values:
1380 V Anode to Cathode,
0,325 A Cathode Current,
Totalling 448 Watts dissipation,
Plus the 140 Watts of filament heating.
{{ short term, on the picture above, it was even 0,4 A at -101V bias, but that was a tad too scary to maintain in the long run … }}
At full load, the power supply voltage sagged from 1700 V DC at idle, down to 1380 at full load (450W). Intriguing, as the transformers in th power supply are a dual set of 800VA toroids.
I managed to make readings of quite a few DC operating points during this session. These will be useful when connecting the push-pull transformer, as they give some insight as to the possible choice of operating point, and provide a verification of the “published” pdf specs, as compared to real life readings.
All tests were conducted in pentode mode, with close to maximum (+/-) allowable S2 Voltage of 600V.