420A

Stable long-life double triode with separate cathodes and center-tapped heater, developed for precision DC-amplifier service where dependable operating characteristics are important.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 2
Base: -
Socket code: UX4
Base pins: 9
Nominal heater: 6.3 V / 360 mA

Description

Double-triode amplifier tube with separate indirectly heated cathodes, center-tapped heater, high stability, and long-life design for d-c amplifiers.

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: -
Socket code: UX4
Base pins: 9
Nominal heater voltage: 6.3 V
Nominal heater current: 360 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

Terminal pinout

Electrical assignments shared by every tube using this base designation.

No verified pinout is recorded for this base designation.

Section ratings

2 physical sections, each with unique specifications.

Section 1

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 140000 Ω
Transconductance: 0.0005 S
Amplification factor: 70
Max plate voltage: 225 V
Max plate dissipation: 0.9 W

Promoted fields mapped from printed maximum-rating and characteristic headings; additional published values preserved in parameter rows. Representative row for repeated identical physical sections.

Section 2

Triode

X-ray radiationInterelectrode capacitances

Plate resistance: 140000 Ω
Transconductance: 0.0005 S
Amplification factor: 70
Max plate voltage: 225 V
Max plate dissipation: 0.9 W

Second physical triode restored under current one-row-per-physical-section policy; identical section.

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

2026 Western Electric 400s

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristic

Plate Current (each section) \ Eh =
110 volts
Plate Current (each section) \ Eh = 110 volts; Ep - -0.6 volt 10.15 milliampere
Transconductance (each section)/ I
500 micromhos
Transconductance (each section)/ I 500 micromhos
Heater-Cathode Voltage
70 volts
Heater-Cathode Voltage 70 volts
Cathode Bias Resistor (Cathodes tied together)
150000 ohms
Cathode Bias Resistor (Cathodes tied together) 150,000 ohms
Plate- Current
0.15 milliampere
Plate- Current 0.15 milliampere
Load Resistance
0.9 megohm
Load Resistance 0.9 megohm
Transconductance
500 micromhos
Transconductance 500 micromhos
equivalent to a
0.26 volt
equivalent to a 0.26 volt change in the output voltmge.)

Other

Plate Dissipation
0.9 watt
Plate Dissipation 0.9 watt