I penny for your thoughts. Come and share your views regarding choice of operating point for the GU81. My initial musings are focused on class AB … around the (already available) voltage of 1500 V DC, with an option to crank it up to 1900 V DC.
So here are the two possible choices that come to my mind:
General remark: The lower anode voltage is limited by 500V and I arbitrarily choose not to allow it to fall below this value. This is due to the maximum V_screen_2 limitation, which is set at 600V.
Assuming a Screen_2 voltage of 500V, I shall not allow the anode to be at a lower potential than the screen, i.e. U_a >= U_s2. This is just as a precaution, so as not to melt the second grid.
The operating points: two envisioned scenarios:
Green scenario (1500V, 100mA):
Peak to peak voltage swing (anode – to – anode ) = 3000V. Raa = 8k. 562 Watts (AB).
Pure class A: 100 mA * 100 mA * 0.5 * 8k = 40 Watts.
Red scenario (1900V, 100mA):
Peak to peak voltage swing = 2000 V; Raa = 5k. 400 Watts (AB).
Pure class A: 100 mA * 100 mA * 0.5 * 5k = 25 Watts.
I penny for your thoughts.
As the tubes are pentodes, it would probably be feasible to make provisions for 40% ultra linear taps on the primary sides of the windings.
Please Kindly Comment.