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.

KT90 Tetrode Vacuum Tube

Also known as KT88

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

TetrodeHeater 6.3 V · 1.6 AOctalEi·JJ 1990

Plate dissipation: 50W
Max plate voltage: 750V
Max screen voltage: 225V
Transconductance: 14mA/V

KT90

Characteristics

Datasheet values, once each. Every value cites its sheet.

HeaterIndirectly heated

Specifications of KT90 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.6 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of KT90 — Limiting values
Plate voltageVa max	750 V
Screen voltageVg2 max	225 V
Plate dissipationPa max	50 W

Mechanical

Specifications of KT90 — Mechanical
Base	Octal
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of KT90 — Small signal
Transconductance	14 mA/V
Plate resistance	11 kΩ
Amplification factor	9

Capacitances

Specifications of KT90 — Capacitances
Input	10 pF
Grid–plate	1.8 pF
Output	29 pF

Charactereditorial reading, not a measurement

Specifications of KT90 — Character
Gain	9%
Power	100%
Drive	89%
Linearity	95%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Using this tube

Applications

High-power output

Generic tetrode power (pp) stage

PA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : EI KT90 datasheet · HiFi CollectiveActive model : Koren pentode

Manufacturer datasheets

1 manufacturer datasheets cross-checked for KT901 verified

KT90 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: EI KT90 datasheet · HiFi Collective
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren pentode

Context

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.

History

Introduced: 1990
Manufacturer: Ei·JJ
Era: Modern

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