309A

Western Electric heater-cathode general-purpose pentode, cross-referenced by the manufacturer to type 24A.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: -
Socket code: UX4
Base pins: 5
Nominal heater: 10 V / 320 mA

Description

Heater-cathode general-purpose pentode; Western Electric table cross-references type 24A.

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: 5
Nominal heater voltage: 10 V
Nominal heater current: 320 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

1 physical section, each with unique specifications.

Section 1

Pentode

X-ray radiationInterelectrode capacitances

Plate resistance: 1000000 Ω
Transconductance: 0.0011 S
Amplification factor: 1100
Max plate voltage: 250 V
Max screen voltage: 100 V

Western Electric 309A indirectly heated variable-mu suppressor-grid pentode for extremely low-noise AF and RF voltage amplification; control gain via grid bias. Heater 10 V 0.32 A, AC or DC; DC heating may lower audio noise. Suppressor grid permanently connected internally to cathode. Absolute published catalog limits plate 250 V, screen 100 V; heater-to-cathode voltage must not exceed 150 V. Typical operating points at screen 75 V and grid -1.5 V: plate 135 V, Ia 4.75 mA, screen 1.1 mA, mu 760, rp 0.7 MΩ, gm 1.09 mA/V; plate 180 V, Ia 4.80 mA, screen 1.1 mA, mu 1100, rp 1.0 MΩ, gm 1.10 mA/V (promoted values); plate 250 V, Ia 4.85 mA, screen 1.1 mA, mu 1450, rp 1.3 MΩ, gm 1.11 mA/V. Direct interelectrode capacitances published: grid-to-plate 0.007 pF, grid-input 5.8 pF, plate-output 14 pF. Manufacturer states small five-pin base with top-cap control-grid terminal, Western Electric 141A five-contact socket; parent socket_code UX4 retained pending master-code reconciliation. At very low signals, improved shielding and noise precautions recommended.

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

1956 Western Electric Tubes

Published operating points and test conditions from this source.

SECTION 1

Pentode

Characteristic

HeaterOrFilamentVoltage
6.3 V
HeaterOrFilamentCurrent
320 mA

Data set 02

2026 Western Electric 300s

Published operating points and test conditions from this source.

SECTION 1

Pentode

Characteristic

Heater voltage
10 volt
Heater voltage 10.0 volts, a.c. or d.c.
Nominal heater current
0.32 ampere
Nominal heater current 0.32 ampere
are shown in Figures
3 volt
are shown in Figures 3 and 4, respectively, as functions of plate voltage for several values of control-
grid voltage and a screen-grid voltage of
75 volt
grid voltage and a screen-grid voltage of 75 volts. Corresponding amplification factor, plate resis
Figures
8 volt
Figures 8 and 9 respectively, for a screen-grid voltage of 75 volts and a plate voltage of 180 volts.
For other plate voltages between
135 volt
For other plate voltages between 135 and 250 volts, the transconductance of a typical tube, for
shown in Figures
10 volt
shown in Figures 10 and 11, respectively, for a screen-grid voltage of 75 volts and several values of
Microphonic Noise—With a plate voltage of
180 volt
Microphonic Noise—With a plate voltage of 180 volts, a screen-grid voltage of 75 volts, a
control-grid bias of
-1.5 volts
control-grid bias of —1.5 volts, and a load resistance of 100,000 ohms, the mean microphonic noise
output level of the
309 volt
output level of the 309A tube, measured in a laboratory reference test set, is 17 db below 1 volt.
Published value
180 volts
180 volts, a screen-grid voltage of 75 volts, a control-grid bias of —1.5 volts, and a load resistance
tubes extends from
112 volt
tubes extends from 112 to 119 db below 1 volt. By reducing the control-grid bias to —1.0 volt and
the screen-grid voltage to
18 volt
the screen-grid voltage to 18 volts, the mean fluctuation noise level may be reduced by about 2.5 db.
HEATER VOLTAGE =
10 VOLT
HEATER VOLTAGE = 10.0 VOLTS
PLATE VOLTAGE =
180 VOLT
PLATE VOLTAGE = 180 VOLTS
SCREEN-GRID VOLTAGE =
75 VOLT
SCREEN-GRID VOLTAGE = 75 VOLTS