What is the KT90 vacuum tube?

The KT90 is a tetrode vacuum tube designed for power (pp) applications. Enhanced KT88..

What is a KT90 substitute or equivalent?

Direct equivalents to the KT90 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 KT90?

Amplification factor μ ≈ 9, transconductance gm ≈ 14 mA/V, plate resistance rp ≈ 11.0 kΩ, max plate voltage 750 V, max plate dissipation 50 W, heater 6.3 V / 1.6 A.

Is the KT90 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT90 as Moderate 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 KT90 sound like?

Enhanced KT88.. 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

←KT90

← KT88 KT99 →Compare → KT88

KT90 Tetrode Vacuum Tube

Tetrode6.3V / 1.6AOctalSPICE

SourceEI KT90 datasheet · HiFi CollectiveReviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

Beam power tetrode rated at 50W for high-power output stages

Datasheet ↗SPICE

KT90 — Ei·JJ — tetrode vacuum tube — (1990)

11.0kΩ

14.0mA/V

10.0pF

1.8pF

29.00pF

GAIN9%

POWER100%

DRIVE89%

LINEARITY95%

SPECIFICATIONS

Heater6.3 V · 1.6 A

Max Plate Voltage750 V

Pa max50 W

Gain Factor9

gm14 mA/V

rp11.0 kΩ

Inter-electrode capacitances

Cgk10 pF

Cgp1.8 pF

Cpk29 pF

PinoutOctal

Era1990

RarityModerate

HEATER6.3V / 1.6A

MAX PLATE750V / 50W

BASEoctal

Source datasheets

1 manufacturer datasheets cross-checked for KT90

1 verified

EXECUTIVE SUMMARY

The KT90 is a indirectly-heated beam tetrode from Ei·JJ, introduced around 1990. It provides a gain factor (μ) of 9 with 11.0kΩ plate resistance. Commonly used in power (pp) applications. Enhanced KT88.

APPLICATIONS

High-power output

Generic tetrode power (pp) stage

• PA/public address

VS KT88

μ +13%Rp -8%Pd +19%Full comparison →

HISTORY

Introduced1990ManufacturerEi·JJ

Modern

KT90 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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