What is the KT99 vacuum tube?

The KT99 is a tetrode vacuum tube designed for power (pp) applications. Premium KT88 derivative. Nice tone, fragile..

What is a KT99 substitute or equivalent?

Direct equivalents to the KT99 include KT88, 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 KT99?

Transconductance gm ≈ 11 mA/V, max plate voltage 700 V, max plate dissipation 42 W, heater 6.3 V / 1.65 A.

Is the KT99 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT99 as Rare 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 KT99 sound like?

Premium KT88 derivative. Nice tone, fragile.. 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 9, 2026

←KT99

← KT90 NR47 →Compare → KT88

KT99 Tetrode Vacuum Tube

Tetrode6.3V / 1.65AOctal

Sourceaudit-we_transmit_gec_other (CLEAN — matches canonical datasheet)Reviewed2026-05-09StatusDataModelCalcModelunder reviewPDF

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

Datasheet ↗

KT99 — Ei·Chinese — tetrode vacuum tube — (1985)

11.0mA/V

15.0pF

1.0pF

8.50pF

GAIN0%

POWER100%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 1.65 A

Max Plate Voltage700 V

Pa max42 W

Gain Factor—

gm11 mA/V

rp—

Inter-electrode capacitances

Cgk15 pF

Cgp1 pF

Cpk8.5 pF

PinoutOctal

Era1985

RarityRare

HEATER6.3V / 1.65A

MAX PLATE700V / 42W

BASEoctal

EXECUTIVE SUMMARY

The KT99 is a indirectly-heated beam tetrode from Ei·Chinese, introduced around 1985. Commonly used in power (pp) applications. Premium KT88 derivative. Nice tone, fragile.

APPLICATIONS

High-power output

Generic tetrode power (pp) stage

• PA/public address

VS KT88

Pd 0%Full comparison →

HISTORY

Introduced1985ManufacturerEi·Chinese

Modern

KT99 Datasheet

Frank's Electron Tube Pages · PDF

↗

METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

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