Hiend Audio, DIY, Hi-Fi, Stereo, Electronics site, for lovers of high-fidelity music reproduction. High-End Vacuum Tubes. Silicon. Do-It-Yourself Audio Systems. Schematics: amplifiers, speakers, horns, CD, DAC. Circuits, Topologies, Acoustics, Cables, Speakers, Voltage Regulators, Equipment Upgrades, Modifications, Problems, Solutions, Tips, Tricks. ------ Dla pasjonatów Hiend Audio, najwyższej wierności odtwarzania muzyki na sprzęcie budowanym, modyfikowanym samemu. Wiedza: elektronika, układy lampowe i krzemowe, wzmacniacze, głośniki, kolumny, tuby, DAC, kable, DIY, porady, sztuczki, problemy, rozwiązania, tor audio.

«

»

Oct 14 2014

Print this Post

RFC: Choice of Operating Point

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:

GU81 pytanie do Ogonowskiego 8k 5k 1900 1500

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.

Z.

Permanent link to this article: http://hiend-audio.com/2014/10/14/rfc-choice-of-operating-point/