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Voltage Tetrode ·Tetrode

448B

High figure-of-merit indirectly heated tetrode for the Western Electric TH radio-relay system, intended for professional high-frequency repeater amplification.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
UX4
Base pins
4
Nominal heater
6.3 V / 450 mA

Description

The 448B is a high figure-of-merit indirectly heated tetrode with plate characteristics approaching those of a pentode, designed primarily for the TH Radio Relay System. It is the aquadag-coated bulb version to suppress fluorescence effects; the 448A, 448B and 454A share the same 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
6.3 V
Nominal heater current
450 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

Tetrode

X-ray radiationInterelectrode capacitances
Plate resistance
33000 Ω
Transconductance
0.0315 S
Max plate voltage
150 V
Max screen voltage
150 V
Max plate dissipation
6 W
Max screen dissipation
1.75 W
Max cathode current
50 mA

Typical values at plate 135 V, screen 135 V, control grid +9.5 V and 323-ohm cathode-bias resistor.

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 400s

Published operating points and test conditions from this source.

SECTION 1

Tetrode

Capacitance

  • Grid-to-Plate Capacitance

    0.03 pF

    Without external shield

  • Input Capacitance

    15.4 pF

    Without external shield

  • Output Capacitance

    2.03 pF

    Without external shield

Other

  • Typical Plate Voltage

    135 V

  • Typical Screen Grid Voltage

    135 V

  • Typical Control Grid Voltage

    9.5 V

  • Cathode Bias Resistor

    323 ohm

  • Plate Current

    24.9 mA

  • Screen Grid Current

    8.8 mA

  • Heater-Cathode Voltage Maximum

    - to 50 V