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Power - Triode ·Triode

261A

Western Electric directly heated power triode for both audio and RF amplification. Published operation includes substantial single-ended Class A audio output and much higher push-pull Class B power, together with transmitting-frequency service.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
UX4
Base pins
4
Nominal heater
10 V / 3.25 A

Description

RF/AF power amplifier, oscillator and modulator triode. The datasheet publishes maximum ratings, typical operating conditions and electrical characteristics.

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
4
Nominal heater voltage
10 V
Nominal heater current
3.25 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
3000 Ω
Transconductance
0.004 S
Amplification factor
12
Max plate voltage
1250 V
Max plate dissipation
100 W
Max cathode current
150 mA

Average characteristics at Eb=1250 V, Ib=68 mA; maximum ratings from same data sheet.

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

1945 United Electronics

Published operating points and test conditions from this source.

SECTION 1

Triode

Characteristics

  • Filament voltage

    10 V

  • Filament current

    3.25 A

Other

  • Maximum direct plate voltage

    1250 V

  • Maximum plate dissipation

    100 W

Data set 02

2026 Western Electric 200s

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

  • Plate To Grid Capacitance

    9 pF

  • Grid To Filament Capacitance

    6.5 pF

  • Plate To Filament Capacitance

    4 pF

Other

  • MaximumGridCurrent

    50 mA

    Direct

  • Maximum RF Grid Current

    5 A

  • Maximum Frequency

    30 MHz

    FullRatings

  • UndistortedOutput

    20 W

    ClassA;PlateVoltage=1250V

  • ApproximateMaximumOutput

    200 W

    ClassB;PushPull;TwoTubes;PlateVoltage=1250V