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Power - Triode (over 1000V 100W) ·Triode

308B

Western Electric directly heated power triode designed for Class A audio amplification. Its low amplification factor and roughly 250 W plate dissipation support substantial linear service, with published single-ended output around 50 W.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
UX4
Base pins
-
Nominal heater
14 V / 6 A

Description

Air-cooled transmitting triode for Class A audio 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
-
Socket code
UX4
Base pins
-
Nominal heater voltage
14 V
Nominal heater current
6 A
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

Triode

X-ray radiationInterelectrode capacitances
Plate resistance
1070 Ω
Transconductance
0.0075 S
Amplification factor
8
Max plate voltage
2250 V
Max plate dissipation
250 W
Max cathode current
325 mA

Promoted fields audited from printed ratings/characteristics; remaining published values preserved as parameters.

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

Triode

Characteristic

  • HeaterOrFilamentVoltage

    14 V

  • HeaterOrFilamentCurrent

    6 A

Other

  • Typical Power Output

    50 W

    ClassA;Audio

Data set 02

2026 Western Electric 300s

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristic

  • Filament voltage

    14 volt

    Filament voltage 14 volts

  • Nominal fi l a m e n t current

    6 amperes

    Nominal fi l a m e n t current 6 amperes

  • Average thermionic emission

    4 amperes

    Average thermionic emission 4 amperes

  • Average Characteristics at

    1500 volts

    Average Characteristics at 1500 volts direct plate potential and minus 150 volts grid bias,

  • A m p l i fi c a t i o n factor

    8

    A m p l i fi c a t i o n factor 8

  • Plate resistance

    1070 ohms

    Plate resistance 1070 ohms

  • Grid to plate tranconductance

    7500 micromhos

    Grid to plate tranconductance 7500 micromhos

  • Direct plate voltage

    1500 volt

    Direct plate voltage 1500

  • Grid bias

    -2 volts

    Grid bias - 2 1 5 — 180 volts

  • Plate dissipation

    240 watts

    Plate dissipation. 240 210 watts

  • Load resistance plate-to-plate

    5200 ohms

    Load resistance plate-to-plate 5200 4280 ohms

  • Load resistance per tube

    1300 ohms

    Load resistance per tube 1300 1070 ohms

  • Direct plate voltage

    1750 volt

    Direct plate voltage 1750 1500 volts

  • Direct plate current

    300 milliamperes

    Direct plate current 300 300 milliamperes

  • Grid bias

    -345 volts

    Grid bias —345 to —460 —300 to —400 volts

  • Nominal power output

    350 watts

    Nominal power output 350 300 watts

  • Direct plate voltage

    1250 volt

    Direct plate voltage 1250 1000 volts

  • Grid bias

    -320 volts

    Grid bias —320 — 260 volts

  • fuse or circuit breaker should remove the plate voltage if the plate current exceeds

    425 volt

    fuse or circuit breaker should remove the plate voltage if the plate current exceeds 425 milliamperes.

  • circuit, reduced plate voltage or a series resistance of

    1000 volt

    circuit, reduced plate voltage or a series resistance of 1000 to 5000 ohms in the plate circuit should

  • A

    5 volt

    A 5% decrease in filament voltage reduces the thermionic emission approximately 25%. Either

  • A resistance of

    30 ohms

    A resistance of 30 to 40 ohms of ten watt rating is suitable.

  • voltages off,

    30 volt

    voltages off, 30% above normal voltage for 10 minutes followed by a longer period at normal voltage.

  • on the basis of

    5 second

    on the basis of 5% second harmonic distortion.

  • the plate voltage. For complete or

    100 volt

    the plate voltage. For complete or 100% modulation, the plate voltage varies from zero to twice

  • the peak power output under

    100 volt

    the peak power output under 100% modulation. In this case, since the plate voltage varies

Other

  • Max. direct plate voltage

    2250 volt

    Max. direct plate voltage 2250 volts

  • Max. direct plate current

    325 milliamperes

    Max. direct plate current 325 milliamperes

  • Max. plate dissipation

    250 watts

    Max. plate dissipation 250 watts

  • Max. direct grid current

    75 milliamperes

    Max. direct grid current 75 milliamperes

  • Max. r-f grid current

    5 amperes

    Max. r-f grid current 5 amperes

  • Max. frequency for the above ratings

    1.5 megacycles

    Max. frequency for the above ratings 1.5 megacycles

  • Max. plate voltage for upper frequency limit of

    4.5 volt

    Max. plate voltage for upper frequency limit of 4.5 Mc 750 volts

  • Max. plate voltage for frequencies between

    1.5 volt

    Max. plate voltage for frequencies between 1.5 and 4.5 Mc in proportion.

  • Max. direct grid current

    75 milliamperes

    Max. direct grid current 75 75 milliamperes