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Tube Tinker — Electron Tube Database
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Voltage Tetrode ·Tetrode

KT21

Output power tetrode designed for receiver audio stages, providing efficient Class-A or Class-AB power amplification from typical receiving-equipment supply voltages.

Directly heatedCold cathodeCommon cathodeDissimilar
Sections
1
Base
-
Socket code
-
Base pins
-
Nominal heater
2 V / 200 mA

Description

High-slope two-volt output tetrode for high stage gain.

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base
-
Socket code
-
Base pins
-
Nominal heater voltage
2 V
Nominal heater current
200 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
Max plate voltage
150 V
Max screen voltage
150 V

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

1955 Marconi

Published operating points and test conditions from this source.

SECTION 1

Tetrode

Characteristic

  • Heater/Filament Voltage

    2 V

  • Heater/Filament Current

    200 mA

Other

  • Maximum/Published Anode Voltage

    150 V

  • Maximum/Published Screen Voltage

    150 V

  • Maximum Published Power Output

    1.25 W

    Two-valve service where applicable

  • Single-Valve Output

    725 mW

    150 V plate and screen

Capacitance

  • Grid-Anode Capacitance

    1.14 pF

  • Anode-Cathode Capacitance

    9.9 pF

  • Grid-Cathode Capacitance

    11 pF