251A

Filamentary air-cooled power triode for high-frequency oscillator or amplifier service, also suitable as a modulator or low-frequency power amplifier. Western Electric data show substantial Class-C RF output and low interelectrode capacitance.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: -
Socket code: MEDIUM5
Base pins: 5
Nominal heater: 10 V / 16 A

Description

Filamentary, air-cooled triode intended for high-frequency oscillator or amplifier service and also usable as a modulator or low-frequency power amplifier. It has low interelectrode capacitance and thoriated-tungsten filament construction.

Socket description

Medium 5-contact transmitting-tube base

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: -
Socket code: MEDIUM5
Base pins: 5
Nominal heater voltage: 10 V
Nominal heater current: 16 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: 2750 Ω
Transconductance: 0.0088 S
Amplification factor: 10.5
Max plate voltage: 3000 V
Max plate dissipation: 1000 W
Max grid dissipation: 50 W
Max cathode current: 600 mA

Average characteristics at Eb=2500 V, Ib=240 mA; maximum ratings from later Western Electric sheet in same PDF.

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 200s

Published operating points and test conditions from this source.

SECTION 1

Triode

Capacitance

Plate To Grid Capacitance
8 pF
Grid To Filament Capacitance
10 pF
Plate To Filament Capacitance
6 pF

Other

Maximum Frequency
30 MHz
FullRatings
Maximum Plate Voltage
2000 V
Frequency=50MHz
Load Impedance
6500 ohm
ClassA;PlateVoltage=2500V;PlateCurrent=240mA
UndistortedOutput
130 W
ClassA;PlateVoltage=2500V
NominalPowerOutput
1200 W
ClassC;PlateVoltage=3000V