What is the KT120 vacuum tube?

The KT120 is a tetrode vacuum tube designed for power (pp) applications. Modern high-power beam..

What is a KT120 substitute or equivalent?

Direct equivalents to the KT120 include KT88. These share the same pinout and operating envelope, so they can usually be swapped without circuit changes — though batch-to-batch variations between manufacturers (NOS vs current production) may shift the sonic character noticeably.

What are the key specifications of the KT120?

Transconductance gm ≈ 12.5 mA/V, plate resistance rp ≈ 3.0 kΩ, max plate voltage 850 V, max plate dissipation 60 W, heater 6.3 V / 1.85 A.

Is the KT120 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT120 as Common availability. NOS (new-old-stock) examples from RCA, Mullard, Tung-Sol, GE, Sylvania and Telefunken trade among collectors; modern production where it exists comes mostly from JJ Electronic, Electro-Harmonix, Tung-Sol (New Sensor), Genalex, and a handful of small-batch makers.

What does the KT120 sound like?

Modern high-power beam.. Sonic character also depends heavily on the circuit operating point, the surrounding tubes in the stage, and the output transformer when present — use the interactive loadline calculator on this page to explore the trade-offs.

By Jean-Michel Falligan Devergne · Reviewed May 29, 2026

←KT120

← GZ34 KT150 →Compare → KT88

KT120 Tetrode Vacuum Tube

Tetrode6.3V / 1.85AOctalSPICE

Sourceaudit-us_b (CLEAN — matches canonical datasheet)Reviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

Beam power tetrode rated at 60W for high-power output stages

Datasheet ↗SPICE

KT120 — Tung-Sol — tetrode vacuum tube — (2009)

3.0kΩ

12.5mA/V

29.0pF

1.8pF

10.00pF

GAIN0%

POWER100%

DRIVE97%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 1.85 A

Max Plate Voltage850 V

Pa max60 W

Gain Factor—

gm12.5 mA/V

rp3.0 kΩ

Inter-electrode capacitances

Cgk29 pF

Cgp1.8 pF

Cpk10 pF

PinoutOctal

Era2009

RarityCommon

HEATER6.3V / 1.85A

MAX PLATE850V / 60W

BASEoctal

Source datasheets

1 manufacturer datasheets cross-checked for KT120

1 verified

EXECUTIVE SUMMARY

The KT120 is a indirectly-heated beam tetrode from Tung-Sol, introduced around 2009. Commonly used in power (pp) applications. Modern high-power beam.

APPLICATIONS

High-power output

Audio Research Reference 75PrimaLuna DiaLogue

• PA/public address

VS KT88

Rp -75%Pd +43%Full comparison →

HISTORY

Introduced2009ManufacturerTung-Sol

Modern