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2A3 — Power Triode, UX4 | Tubeofile
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2A3
Power Triode — DHT — UX4
···
+ Compare
RCA
↗ r-type.org
↗ TDSL
↗ Radiomuseum
Known Equivalents & Substitutes
VT-95
CV1831
KX2A3
NU-2A3
2A3W
2A3H
6A3
ZA3W
5930
AC042
2S4S
Similar Tubes (Not Drop-In Compatible)
300B
Directly heated power triode with similar application but higher power (8W SE), different base and filament (5V/1.2A)
45
Directly heated power triode on UX4 base, lower power (1.6W SE), lower filament current (1.5A at 2.5V)
6A5G
Single-plate version of 2A3 with Octal base; electrically similar but not pin-compatible with UX4 2A3
6B4G
Same electrical characteristics (mu=4.2, 3.5W SE) but Octal base instead of UX4
PX4
British directly heated power triode (Osram), similar power class (3.5W SE) but 4V filament and different base
Electrical Specifications
Absolute Maximum
Anode Voltage (max)
Max. Plate Voltage
300
V
Anode Dissipation (max)
Max. Plate Dissipation
15
W
Max Grid Resistor
Max. Grid Resistor (fixed bias)
0.05
MΩ
Max Grid Resistor
Max. Grid Resistor (cathode bias)
0.5
MΩ
Typical Operating
Notes
Introduced by RCA in 1933 as a replacement for the type 45, offering approximately double the power output.
Original versions used two parallel plates; later production used a single plate.
The 6A3 is the 6.3V heater version on UX4 base, directly interchangeable with heater supply change.
The 5930 is a ruggedized military version with higher max plate voltage rating (360V vs 300V).
Classic single-ended Class A audio output tube, typically delivering 3.5W into a 2500 ohm load.
The 2S4S (2C4C) is the Soviet-era Russian equivalent.
Pin Layout — UX4
1
2
3
4
1
Filament (f+)
2
Plate
3
Grid
4
Filament (f-)
Socket-Compatible Tubes
⚠ Not electrically compatible
26
300B
45
71A
801A
VT-25
VT-52
References
https://frank.pocnet.net/sheets/049/2/2A3.pdf
https://frank.pocnet.net/sheets/021/2/2A3.pdf
Anode Voltage (typical)
Plate Voltage
250
V
Grid 1 Bias Voltage
Grid Voltage
-45
V
Anode Current
Plate Current
60
mA
Anode Resistance
Plate Resistance
800
Ω
Transconductance
Transconductance
5.25
mA/V
Amplification Factor (μ)
Amplification Factor
4.2
—
Cathode Resistor (self-bias)
Cathode Resistor (self-bias)
750
Ω
Output
Output Power
Power Output
3.5
W
Load Impedance
Load Resistance
2,500
Ω
Capacitances
Grid-to-Plate Capacitance
Grid-to-Plate Capacitance
16.5
pF
Grid-to-Cathode Capacitance
Grid-to-Filament Capacitance
7.5
pF
Anode-to-Cathode Capacitance
Plate-to-Filament Capacitance
5.5
pF
Heater
Heater Voltage
Filament Voltage
2.5
V
Heater Current
Filament Current
2.5
A