811A is direct-heated type thorium tungsten cathode high µ triode, can be used as high-frequency oscillation power amplification.
811 is similar to 811A, they can be exchanged each other.

Heater
Uf--------------------------------------6.3 V
If---------------------------------------4 A 
Maximum Rating
Ua--------------------------------------1250 V
Ia---------------------------------------125 mA
Pa--------------------------------------40W
grid current---------------------------------------50 mA
Operating frequency and Ua
When the operating frequency above 30MC, Ua and anode input power should be reduced as follows: 
Operating frequency(MC) Ua and anode input power
60 89%
80 70%
100 55%
 When it is in constant working, the anode should not be allowed to have slight red; when in interrupted working, it should only be allowed to have perceptible slight red.
Direct Interelectrode Capacitances 
Input--------------------------------------5.5 PF
output--------------------------------------0.6 PF
Grid to plate……………………………………………..5.5 PF
Static parameter:
Ua……………………………………………………….2000 V
-Ug……………………………………………………...2 V
Ia………………………………………………………26 mA
µ(Ia=20mA)……………………………………..160
Maximum rating in other operating conditions
R-F power amplifier or oscillation, C amplifier (CW)
                     CCS          ICAS
 Ua………………………………….1250            1500   V
 Ia……………………………………175             175    Ma
 Pa…………………………………..45              65     W
 Pa (in)……………………………..175            260     W
 Ug…………………………………-200            -200     V
 Ig…………………………………..55               50     mA
C amplifier anode-modulation, R-F power amplifier
                     CCS          ICAS
Ua…………………………………1000          1250    V
Ia…………………………………..125           150   mA
Pa………………………………….30            45    W
Pa (in)……………………………115          175    W
Ug…………………………………-200         -200    V
Ig……………………………………50           50     mA
CCS: constant working 
ICAS: interrupted working