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.

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

←KT88

← KT77 KT90 →Compare → 6550

KT88 Tetrode Vacuum Tube

Tetrode6.3V / 1.6AOctalSPICE

SourceGEC datasheetReviewed2026-05-29StatusDataModelCalcModelKoren v1PDF

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

Datasheet ↗SPICE

KT88 — GEC — tetrode vacuum tube — (1956)

12.0kΩ

11.5mA/V

16.0pF

1.5pF

11.00pF

GAIN8%

POWER100%

DRIVE88%

LINEARITY95%

SPECIFICATIONS

Heater6.3 V · 1.6 A

Max Plate Voltage800 V

Pa max42 W

Gain Factor8

gm11.5 mA/V

rp12.0 kΩ

Inter-electrode capacitances

Cgk16 pF

Cgp1.5 pF

Cpk11 pF

PinoutOctal

Era1956

RaritySought-after

HEATER6.3V / 1.6A

MAX PLATE800V / 42W

BASEoctal

Source datasheets

3 manufacturer datasheets cross-checked for KT88

3 verified

Triode-connectedJJ Electronicnon datée (production moderne)

Specs when the screen grid (g2) is tied to the anode — the tube acts as a triode.

Vg1

15 V

According to JJ Electronic (www.jj-electronic.sk) (non datée (production moderne)): « Triode Connected »

EXECUTIVE SUMMARY

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.

APPLICATIONS

High-power output

Dynaco Mark IIIMcIntosh MC275Audio Research VT100

• Guitar amp• PA/public address

VS 6550

μ 0%Rp +0%Pd +20%Full comparison →

HISTORY

Introduced1956ManufacturerGEC

Golden Age