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Power - Triode ·Triode

2A3

Classic directly heated low-mu audio power triode for single-ended and push-pull output stages. Its low plate resistance, roughly 15 W plate dissipation, and typical 250 V operating conditions made it a standard high-quality audio output tube.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
4D
Socket code
UX4
Base pins
4
Nominal heater
2.5 V / 2.5 A

Description

Directly heated power-amplifier triode for Class-A and push-pull Class-AB audio output service.

Socket description

Medium-shell UX 4-contact

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
4D
Socket code
UX4
Base pins
4
Nominal heater voltage
2.5 V
Nominal heater current
2.5 A
Parallel heater voltage
-
Parallel heater current
-
Series capable
No

4D - Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

1 physical section, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
800 Ω
Transconductance
0.00525 S
Amplification factor
4.2
Max plate voltage
300 V
Max plate dissipation
15 W
Max cathode current
100 mA

Class A1 power triode; representative characteristics at 250 V plate.

Source-dependent data

Operating conditions by source

Each block preserves the test conditions and published values from one reference. Values from different sources are intentionally kept separate.

Data set 01

1937 Raytheon Radio Receiving Tubes

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Maximum plate voltage

    300 V

    Published datasheet rating

  • Plate voltage

    250 V

    ClassA

  • Control-grid bias

    45 V

    ClassA

  • Plate current

    60 mA

    ClassA

  • Load resistance

    2500 ohm

    ClassA

  • Power output

    3.5 W

    ClassA

  • Push-pull plate voltage

    300 V

    ClassAB PushPull TwoTubes

  • Push-pull fixed-bias grid voltage

    62 V

    ClassAB PushPull TwoTubes

  • Push-pull no-signal plate current per tube

    40 mA

    ClassAB PushPull TwoTubes

  • Push-pull load resistance fixed bias

    3000 ohm

    ClassAB PushPull TwoTubes

  • Push-pull power output fixed bias

    15 W

    ClassAB PushPull TwoTubes

  • Push-pull load resistance self bias

    5000 ohm

    ClassAB PushPull TwoTubes

  • Push-pull power output self bias

    10 W

    ClassAB PushPull TwoTubes

Characteristic

  • Plate resistance

    800 ohm

    Published datasheet characteristic

  • Transconductance

    5250 µS

    Published datasheet characteristic

  • Amplification factor

    4.2

    Published datasheet characteristic

  • Heater/filament voltage

    2.5 V

    Published heater/filament rating

  • Heater/filament current

    2.5 A

    Published heater/filament rating

Data set 02

1940 RCA

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • FiLaMENT VoLTAGE (A. C.or D. C)..ovviiinnn,

    2.5 V

    FiLaMENT VoLTAGE (A. C.or D. C)..ovviiinnn, 2.5 Volts

  • FILAMENT CURRENT .......oc

    2.5 A

    FILAMENT CURRENT .......oc0n... esseisneanas 2.5 Amperes

  • FILAMENT VOLTAGE (A. C).vvvveiniinennnns

    2.5 V

    FILAMENT VOLTAGE (A. C).vvvveiniinennnns 2.5 Volts

  • PLATE VOLTAGE .+ iviveineareenananenrnonnennns

    250 V

    PLATE VOLTAGE .+ iviveineareenananenrnonnennns 250 max. Volts

  • GRID VOLTAGE¥* ......c.civvvanns e —

    45 V

    GRID VOLTAGE¥* ......c.civvvanns e —45 Volts

  • PLATE CURRENT ttvvivnuneennnernnennnnnnnnnns

    50

    PLATE CURRENT ttvvivnuneennnernnennnnnnnnnns 50 Milliamperes

  • AMPLIFICATION FACTOR ........ceviinenvenennns

    2

    AMPLIFICATION FACTOR ........ceviinenvenennns 4,2

  • SELF-BIAS RESISTOR . ..vivvcnvnnrnnenrennnnennnn

    750 ohm

    SELF-BIAS RESISTOR . ..vivvcnvnnrnnenrennnnennnn 750 Ohms

  • UNDISTORTED POWER OUTPUT....cvvvvvvvnennnn

    35 W

    UNDISTORTED POWER OUTPUT....cvvvvvvvnennnn. 35 Watts

  • FILAMENT VOLTAGE (A. C.)...ovuvnvvnn

    2.5 V

    FILAMENT VOLTAGE (A. C.)...ovuvnvvnn.. 2.5 2.5 Volts

  • Prate VoLTAGE (Maximum).......v

    300 V

    Prate VoLTAGE (Maximum).......v...... 300 300 Volts

  • GRID VOLTAGE* ...... vevercovanerconns —

    62 V

    GRID VOLTAGE* ...... vevercovanerconns —62 — Volts

  • SELF-BIAS RESISTOR ..ecvnvevenn. teeeraenn —

    780 ohm

    SELF-BIAS RESISTOR ..ecvnvevenn. teeeraenn — 780 Ohms

  • ZEerO-SIGNAL PLATE CURRENT (Per tube)

    40

    ZEerO-SIGNAL PLATE CURRENT (Per tube)... 40 40 Milliamperes

  • POWER OUTPUT .i.vvereennnccesonnnnns

    10 W

    POWER OUTPUT .i.vvereennnccesonnnnns 15 10 Watts

  • * Grid volts measured from m}d:;;r;ir;t'

    1 V

    * Grid volts measured from m}d:;;r;ir;t' 1;{' ;-c operated filament.

  • As a power amplifier (Class A;), the

    2

    As a power amplifier (Class A;), the 2A3 is usable either singly or in push-

  • value makes the

    2

    value makes the 2A3 somewhat critical as to grid-bias voltage, since a very small

  • grid circuit should not exceed

    0.5

    grid circuit should not exceed 0.5 megohm. With fixed-bias, however, the d-c

Characteristic

  • PLATE RESISTANCE . ..iiviiernennnennnrnnnnnns

    800 ohm

    PLATE RESISTANCE . ..iiviiernennnennnrnnnnnns 800 Ohms

  • TRANSCONDUCTANCE .. .ivnrvvnnnanecnnnancanns

    5250 µS

    TRANSCONDUCTANCE .. .ivnrvvnnnanecnnnancanns 5250 Micromhos

  • LOAD RESISTANCE + ..t vvvvrcnnnnnnnnnennennsnns

    2500 ohm

    LOAD RESISTANCE + ..t vvvvrcnnnnnnnnnennennsnns 2500 Ohms

  • ErrecTIVE LoAD RESISTANCE (Plate-to-plate)

    5000 ohm

    ErrecTIVE LoAD RESISTANCE (Plate-to-plate) 3000 5000 Ohms

  • very high transconductance of these tubes—

    5250 µS

    very high transconductance of these tubes—5250 micromhos. This very high

  • resistance should not exceed

    50000 ohm

    resistance should not exceed 50000 ohms.

Data set 03

1948 Brimar Radio Valve Manual

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristic

  • HeaterOrFilamentVoltage

    2.5 V

  • HeaterOrFilamentCurrent

    2.5 A

Other

  • Power Output

    3.5 W

    ClassA

Data set 04

1950 Sylvania

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristic

  • Tension filament CA. ou CC. ... ... .. .. .. 2,5 Volts

    2.5 V

    Tension filament CA. ou CC. ... ... .. .. .. 2,5 Volts

  • Courant filament ... ... ... . . 0 e 2,5 ampéres

    2.5 A

    Courant filament ... ... ... . . 0 e 2,5 ampéres

Data set 05

1958 Brimar Radio Valve No 7

Published operating points and test conditions from this source.

SECTION 1

Triode

Other

  • Power output

    3.5 W

    ClassA

Data set 06

195X General Electric Essential Characteristics

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

  • Input capacitance

    7.5 pF

    Section1

  • Output capacitance

    5.5 pF

    Section1

  • Grid-to-plate capacitance

    16.6 pF

    Section1

Other

  • Plate voltage

    250 V

    ClassA

  • Control-grid voltage

    -45 V

    ClassA

  • Plate current

    60 mA

    ClassA

  • Load resistance

    2500 Ω

    ClassA

  • Power output

    3.5 W

    ClassA

  • Plate voltage

    300 V

    ClassAB PushPull TwoTubes

  • Plate current

    80 mA

    ClassAB PushPull TwoTubes

  • Load resistance

    3000 Ω

    ClassAB PushPull TwoTubes

  • Power output

    15 W

    ClassAB PushPull TwoTubes

Characteristic

  • Plate resistance

    800 Ω

    ClassA

  • Transconductance

    5250 µS

    ClassA

  • Amplification factor

    4.2

    ClassA

Data set 07

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

  • Grid To Plate Capacitance

    16.5 pF

    DirectInterelectrode

  • Input Capacitance

    7.5 pF

    DirectInterelectrode

  • Output Capacitance

    5.5 pF

    DirectInterelectrode