398A

Western Electric 5603/398A filamentary power pentode amplifier with design-center ratings and documented power-amplifier operating conditions. Its directly heated construction is intended for output-stage service.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: B8-11
Socket code: IO
Base pins: 8
Nominal heater: 6.5 V / 500 mA

Description

The 5603/398A is a filamentary power pentode amplifier. The sheet gives design-center ratings and an operating condition for power-amplifier service.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: B8-11
Socket code: IO
Base pins: 8
Nominal heater voltage: 6.5 V
Nominal heater current: 500 mA
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

B8-11 - 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

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 17000 Ω
Transconductance: 0.0054 S
Amplification factor: 92
Max plate voltage: 150 V
Max screen voltage: 150 V
Max plate dissipation: 8 W
Max screen dissipation: 2 W
Max cathode current: 75 mA

Typical characteristics at plate 135 V and screen 135 V: plate current 50 mA, screen current 4 mA, amplification factor 92, plate resistance 17 kohm and transconductance 5400 uS.

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 300s

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

ControlGridToFilamentScreenSuppressorCapacitance
9.5 pF
PlateToControlGridCapacitance
0.3 pF
PlateToFilamentScreenSuppressorCapacitance
7.5 pF
Cathode Bias Resistor
230 ohm
SignalGridVoltage
8.5 V AC
Load Resistance
2500 ohm

Characteristic

Plate Current
50 mA
Plate=135 V; Screen=135 V
Screen Current
4 mA
Plate=135 V; Screen=135 V
Power Output
2.2 W

Data set 02

2026 Western Electric Other

Published operating points and test conditions from this source.

SECTION 1

Pentode

Other

Plate Voltage Maximum
150 V
Design-center value
Plate Dissipation Maximum
8 W
Design-center value
Screen Voltage Maximum
150 V
Design-center value
Screen Dissipation Maximum
2.5 W
Design-center value
Cathode Current Maximum
75 mA
Design-center value
Filament Voltage
6.3 V
Operating conditions and characteristics
Filament Current
500 mA
Operating conditions and characteristics
Plate Voltage
135 V
Published operating condition
Screen Voltage
135 V
Published operating condition
Suppressor-Grid Voltage
0 V
Published operating condition
Cathode Bias Resistor
230 ohm
Published operating condition
Signal Grid Voltage
8.5 V ac
Published operating condition
Load Resistance
2500 ohm
Published operating condition

Characteristic

Plate Current
50 mA
Published operating condition
Screen Current
4 mA
Published operating condition
Amplification Factor
92
Published operating condition
Plate Resistance
17000 ohm
Published operating condition
Transconductance
5400 uS
Published operating condition
Power Output
2.2 W
Published operating condition

Capacitance

Control-grid to filament/screen/suppressor capacitance
9.5 pF
No shield
Plate to control-grid capacitance
0.3 pF
No shield
Plate to filament/screen/suppressor capacitance
7.5 pF
No shield