71A

Power Triode — DHT — UX4

RCA

Known Equivalents & Substitutes

171A7171BUX171ACX371ACX71ACV2541182B482B

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Plate Voltage (max)180V

Max Grid ResistorGrid Circuit Resistance (max)0.5MΩ

Typical Operating

Anode Voltage (typical)Plate Voltage180V

Grid 1 Bias VoltageGrid Voltage-40.5V

Anode CurrentPlate Current20mA

Anode ResistancePlate Resistance1,750Ω

TransconductanceTransconductance

Output

Output PowerUndistorted Power Output0.79W

Load ImpedanceLoad Resistance4,800Ω

Capacitances

Grid-to-Plate CapacitanceGrid-to-Plate Capacitance7.5pF

Grid-to-Cathode CapacitanceGrid-to-Filament Capacitance3.2pF

Anode-to-Cathode CapacitancePlate-to-Filament Capacitance2.9pF

Heater

Heater VoltageFilament Voltage5V

Heater CurrentFilament Current0.25A

Notes

Pa_max is not stated in any US manufacturer datasheet (RCA, Tung-Sol, Cunningham). Community consensus suggests approximately 4W but this is not an official rating.
DHT tube: the filament serves as the cathode; there is no heater-cathode isolation.
For operation on a-c filament supply, increase grid-bias voltage 2.5 volts. The d-c resistance in the grid circuit should not exceed 0.5 megohm.
Grid bias return should be made to the negative filament terminal (pin 4) when using DC filament supply.
The 71 and 71B are direct substitutes (Sams Handbook); 71A replaced the earlier 171A/UX171A designation.

Pin Layout — UX4

1Filament (f-)

2Plate (Anode)

3Grid

4Filament (f+)

Socket-Compatible Tubes ⚠ Not electrically compatible

References