TUBEOFILE
12A — Small Signal Triode, UX4 | Tubeofile
Known Equivalents & Substitutes
Similar Tubes (Not Drop-In Compatible)
Successor DHT triode on UX4 base with 5V filament, same mu (8) but lower plate resistance (10kΩ vs 20kΩ) and higher gm — largely replaced the 12A in later designs Contemporary DHT triode on UX4 base with 1.5V filament, similar low-mu characteristics (mu=8.3), used in similar amplifier applications Electrical Specifications
Absolute Maximum
Anode Voltage (max) Max Plate Voltage 180V
Anode Dissipation (max) Plate Dissipation (max) 0.5W
Typical Operating
Anode Voltage (typical) Plate Voltage 90V
Grid 1 Bias Voltage Grid Voltage -4.5V
Notes
The 12A is an early 1920s directly heated triode from the transition period between bright-emitter and oxide-coated filament designs. TDSL lists 112A, CV907, G112, and PX1120 as close or identical substitutes. The type 12 is listed as a different rating/performance variant. Filament is 5V at 0.25A — designed for battery operation. The low filament current was a key advantage over earlier types. Typical operating conditions: Va=90V, Vg=-4.5V, Ia=1.7mA (detector/amplifier service per RCA data). The 12A was gradually superseded by the 01A (type 201A) which offered improved performance with the same base and filament voltage. Pin Layout — UX4
1 2 3 4
1 Filament (f+)
2 Plate
3 Grid
4 Filament (f-)
Socket-Compatible Tubes ⚠ Not electrically compatible
Anode Current Plate Current
1.7mA
Anode Resistance Plate Resistance 20,000Ω
Transconductance Transconductance 0.4mA/V
Amplification Factor (μ) Amplification Factor 8—
Heater
Heater Voltage Filament Voltage 5V
Heater Current Filament Current 0.25A