What is the KT88 vacuum tube?

The KT88 is a tetrode vacuum tube designed for power (pp) applications. Commanding authority..

What is a KT88 substitute or equivalent?

Direct equivalents to the KT88 include 6550. 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 KT88?

Amplification factor μ ≈ 8, transconductance gm ≈ 11.5 mA/V, plate resistance rp ≈ 12.0 kΩ, max plate voltage 800 V, max plate dissipation 42 W, heater 6.3 V / 1.6 A.

Is the KT88 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT88 as Sought-after 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 KT88 sound like?

Commanding authority.. 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.

KT88 Tetrode Vacuum Tube

Also known as 6550

Beam power tetrode rated at 42W for high-power output stages

TetrodeHeater 6.3 V · 1.6 AOctalGEC 1956

Plate dissipation: 42W
Max plate voltage: 800V
Transconductance: 11.5mA/V

KT88

Characteristics

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

HeaterIndirectly heated

Specifications of KT88 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.6 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of KT88 — Limiting values
Plate voltageVa max	800 V
Plate dissipationPa max	42 W

Mechanical

Specifications of KT88 — Mechanical
Base	Octal
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of KT88 — Small signal
Transconductance	11.5 mA/V
Plate resistance	12 kΩ
Amplification factor	8

Capacitances

Specifications of KT88 — Capacitances
Input	16 pF
Grid–plate	1.5 pF
Output	11 pF

Charactereditorial reading, not a measurement

Specifications of KT88 — Character
Gain	8%
Power	100%
Drive	88%
Linearity	95%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	B+	Va	Vg2	Vg1 / Rk	Ia	Ig2	Load	Pout	THD	gm	μ	rp	Source
triode connection, single-endedclass not stated · fixed bias		250 V			143 mA					12 mA/V	8	670 Ω	OCR, to be checked Genalex / The M-O Valve Company Limited · 1974 · p. 2 · transcript
Class AB1, push-pullpentode connection · cathode bias	560 V		300 V	-30 V	64 mA	1.7 mA	9 kΩ a-a	50 W	3%				OCR, to be checked Genalex / The M-O Valve Company Limited · 1974 · p. 2 · transcript
ultra-linear, push-pullclass not stated · cathode bias	500 V	425 V	425 V	-50 V	87 mA		6 kΩ a-a	50 W	1%				OCR, to be checked Genalex · 1959 · p. 2 · transcript
triode connection, push-pullclass not stated · cathode bias	400 V	350 V		-38 V	67 mA		4 kΩ a-a	15 W					OCR, to be checked Genalex · 1959 · p. 2 · transcript

Using this tube

Applications

High-power output

Dynaco Mark IIIMcIntosh MC275Audio Research VT100

Guitar ampPA/public address

Featured in these amplifiers

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : GEC datasheetActive model : Koren v1

Manufacturer datasheets

3 manufacturer datasheets cross-checked for KT883 verified

Triode-connectedJJ Electronicnon datée (production moderne)

Vg1: 15 V
µ: 8

KT88 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: GEC datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren v1

Context

The KT88 is a beam tetrode developed by GEC/Marconi-Osram (MOV) in 1956, designed specifically for high-power audio amplifier service with a plate dissipation of 42W. It produces 50W or more per pair in push-pull with a sound that combines the linearity of a triode with the power and efficiency of a beam tetrode, delivering tight bass, controlled dynamics, and a somewhat neutral tonal balance. The KT88 is the output tube of the legendary Dynaco Mark III, McIntosh MC275, and many other classic amplifiers. Original GEC KT88s are among the most valuable NOS audio tubes; Gold Lion (Genalex reissue), Shuguang, and JJ produce current alternatives of varying quality.

History

Introduced: 1956
Manufacturer: GEC
Era: Golden Age

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