26

Small Signal Triode — DHT — UX4

RCA

Known Equivalents & Substitutes

226UX226CX326CV943REN326

Electrical Specifications

Absolute Maximum

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

Typical Operating

Anode Voltage (typical)Plate Voltage180V

Grid 1 Bias VoltageGrid Voltage-14.5V

Anode CurrentPlate Current6.2mA

Anode ResistancePlate Resistance7,300Ω

TransconductanceTransconductance

Capacitances

Grid-to-Plate CapacitanceGrid-Plate Capacitance8.1pF

Grid-to-Cathode CapacitanceGrid-Filament Capacitance2.8pF

Anode-to-Cathode CapacitancePlate-Filament Capacitance2.5pF

Heater

Heater VoltageFilament Voltage1.5V

Heater CurrentFilament Current1.05A

Notes

Directly heated triode — filament is the cathode. No separate heater-cathode insulation; Vhk_max is not applicable.
Grid voltage is measured from the mid-point of the AC-operated filament.
The coated filament should be operated at exactly 1.5V via a step-down transformer. Designed specifically for AC filament operation (unlike the earlier UX-201A which used thoriated tungsten).
Original 1920s production used globe-shaped envelopes (UX-226); later production (1930s onward) used ST-14 bulbs. Both are electrically identical.
High plate resistance (7.3 kOhm) limits its usefulness as a driver for power tubes — a step-down interstage transformer is recommended for low output impedance.
No maximum plate dissipation rating is specified in the original RCA datasheet. At the maximum rated operating point (180V, 6.2mA), plate dissipation is approximately 1.1W.

Pin Layout — UX4

1Filament

2Plate (Anode)

3Grid

4Filament

Socket-Compatible Tubes ⚠ Not electrically compatible

References