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.
Same UX5 base and pinout, higher mu (13.8 vs 9) and different heater (2.5V/1.0A vs 2.5V/1.75A). Sams lists as substitute.
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Maximum Plate Voltage275V
Cathode Current (max)Maximum DC Plate Current5mA
Heater-to-Cathode Voltage (max)Maximum Heater-Cathode Voltage90V
Typical Operating
Anode Voltage (typical)Plate Voltage250V
Notes
Indirectly heated cathode — the 5th pin (cathode) is separate from the heater, unlike the directly heated type 26.
Maximum heater-to-cathode voltage is 90V. Exceeding this damages the heater-cathode insulation.
Maximum DC plate current limited to 5.0 mA per the Tung-Sol datasheet. No explicit maximum plate dissipation rating is given in any manufacturer datasheet consulted. At the maximum rated operating point (250V, 5.2 mA, Vg = -21V), plate dissipation is approximately 1.2W.
Original 1927 production (UY-227) used globe-shaped S-14 envelopes; production changed to ST-12 bulbs around 1931-32. Both are electrically identical.
Grid resistor for detector service: minimum 0.5 MΩ, maximum 0.5 MΩ (biased); grid leak detector uses return to cathode with 250 pF grid condenser.
Pin Layout — UX5
1Heater
2Anode (Plate)
3Control Grid
4Cathode
5
Socket-Compatible Tubes ⚠ Not electrically compatible