Data: MediumMedium quality — at least 60% of universal parameters and pins are present, but some key data is missing. Verify specific values against datasheets before critical use.
Max Grid ResistorGrid Circuit Resistance (max)0.5MΩ
Typical Operating
Anode Voltage (typical)Plate Voltage180V
Grid 1 Bias VoltageGrid Voltage-40.5V
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