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KT120

High-power beam tetrode designed primarily for high-fidelity audio output, with 60-watt plate dissipation and push-pull designs reaching approximately 200 watts.

Directly heatedCold cathodeCommon cathodeDissimilar

Sections: 1
Base: 7AC
Socket code: IO
Base pins: 8
Nominal heater: 6.3 V / 1.95 A

Description

High-power beam tetrode for low-frequency power amplification in HI-FI audio output stages.

Socket description

International Octal

General specifications

Tube and section characteristics

Properties common to every published source and operating point.

Heater and base

Base: 7AC
Socket code: IO
Base pins: 8
Nominal heater voltage: 6.3 V
Nominal heater current: 1.95 A
Parallel heater voltage: -
Parallel heater current: -
Series capable: No

7AC - Terminal pinout

Electrical assignments shared by every tube using this base designation.

Terminal	Section	Connection	Evidence
PIN1Pin 1	—	NC	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN2Pin 2	—	H — Heater	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN3Pin 3	A	P — Plate (Anode)	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN4Pin 4	A	G2 — Screen Grid	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN5Pin 5	A	G1 — Control Grid	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN7Pin 7	—	H — Heater	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN8Pin 8	A	BP — Beam-Forming PlateGroup AC8	Verified 12L6GT/25L6GT manufacturer basing, 7AC
PIN8Pin 8	A	K — CathodeGroup AC8	Verified 12L6GT/25L6GT manufacturer basing, 7AC

Section ratings

1 physical section, each with unique specifications.

Section 1

Beam Power

X-ray radiationInterelectrode capacitances

Plate resistance: 3000 Ω
Transconductance: 0.0125 S
Max plate voltage: 850 V
Max screen voltage: 650 V
Max plate dissipation: 60 W
Max screen dissipation: 8 W
Max cathode current: 250 mA

850-V plate rating is tetrode connection; 650-V screen rating is pentode connection. Alternate connection limits retained as parameters.

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

1961 Tung Sol

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Other

Heater voltage
6.3 V
Heater current minimum
1.7 A
Heater current maximum
1.95 A
Triode-connection maximum plate voltage
650 V
TriodeConnection
Triode/ultralinear maximum grid-2 voltage
600 V
TriodeConnection
Cathode current maximum
230 mA
TriodeConnection
Maximum signal power output minimum
20 W
ClassA1
Total harmonic distortion maximum
14 %
ClassA1

Capacitance

Grid-1-to-plate capacitance
1.8 pF
Input capacitance
29 pF
Output capacitance
10 pF

Characteristic

Plate current minimum
135 mA
ClassA1
Plate current maximum
165 mA
ClassA1
Grid-2 current maximum
14 mA
ClassA1

Data set 02

2026 Tungsol Rebrand

Published operating points and test conditions from this source.

SECTION 1

Beam Power

Application

Application
HighPowerAudioOutput text