GU21B
TRIODE
The GU21 B triode is designed for use as an amplifier or oscillator tube at frequencies up to 26 MHz in groundedgrid circuits and in circuits with neutralization.
GENERAL
Cathode: directly heated, carbonized thonated tungsten.
Envelope: glasstometal with grid ring.
Cooling: forced air.
Height: at most 355 mm.
Diameter: at most 142 mm.
Mass: at most 8 kg.
OPERATING ENVIRONMENTAL CONDITIONS  
Ambient temperature, °C  10 to 55 
Relative humidity at up to +25°25, %  98 
BASIC DATA Electrical Parameters 

Filament voltage, V  8.3 
Filament current, A  140160 
Mutual conductance (at anode voltage 2 kV, anode currents 2 and 4 A), mA/V  2535 
Gain coefficient (at anode voltages 2 and 5 kV and anode current 2 A)  4155 
Anode current at zero grid voltage (at anode voltage 5 kV), A  1.12.3 
Interelectrode capacitance, pF:  
input, at most  55 
output, at most  1.5 
transfer, at most  45 
Limit Operating Values  
Filament voltage, V  7.88.3 
Anode voltage, kV  9 
Filament starting current, A  225 
Dissipation, W:  
anode  1.0x10_{4} 
grid  600 
Operating frequency, MHz  26 
Temperature at envelope, stem and seals, °C  150 