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Power - Triode ·Triode

300BXLS

Heavy-duty directly heated 300B-family audio triode for substantially higher Class A output. Approximately 60 W plate dissipation, elevated plate-voltage capability, and higher operating current extend the familiar low-mu 300B concept into more powerful stages.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
UX4
Socket code
UX4
Base pins
4
Nominal heater
5 V / 1.5 A

Description

300B-XLS high-power directly heated 300B-family audio triode. The supplied Emission Labs sheet was read for filament data, maximum ratings, representative operating points, gm/rp/mu, output conditions, capacitances, and rectifier filter conditions as applicable.

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

UX4 - 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
700 Ω
Transconductance
0.0064 S
Amplification factor
4.5
Max plate voltage
600 V
Max plate dissipation
60 W
Max cathode current
120 mA

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 Emission Labs

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristics

  • Filament voltage

    5 V

  • Filament current

    1.5 A

  • Plate resistance

    700 ohm

    ClassA

  • Amplification factor

    4.5

    ClassA

  • Transconductance

    6400 uS

    ClassA

Other

  • Plate voltage

    495 V

    ClassA

  • Plate current

    100 mA

    ClassA

  • Grid voltage

    -104 V

    ClassA

  • Peak plate dissipation

    60 W