What is the KT63 vacuum tube?

The KT63 is a tetrode vacuum tube designed for power (se) applications. British vintage pentode. Warm midrange..

What is a KT63 substitute or equivalent?

Direct equivalents to the KT63 include 6F6. 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 KT63?

Transconductance gm ≈ 2.5 mA/V, plate resistance rp ≈ 80.0 kΩ, max plate voltage 250 V, max plate dissipation 11 W, heater 6.3 V / 0.7 A.

Is the KT63 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT63 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 KT63 sound like?

British vintage pentode. Warm midrange.. 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

←KT63

← KT61 KT66 →Compare…

KT63 Tetrode Vacuum Tube

Tetrode6.3V / 0.7AOctal

SourceGEC·MOVReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

Beam power tetrode rated at 11W for high-power output stages

Datasheet ↗

KT63 — GEC·MOV — tetrode vacuum tube — (1940)

80.0kΩ

2.5mA/V

9.8pF

0.8pF

9.00pF

GAIN0%

POWER28%

DRIVE20%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 0.7 A

Max Plate Voltage250 V

Pa max11 W

Gain Factor—

gm2.5 mA/V

rp80.0 kΩ

Inter-electrode capacitances

Cgk9.8 pF

Cgp0.8 pF

Cpk9 pF

PinoutOctal

Era1940

RarityModerate

HEATER6.3V / 0.7A

MAX PLATE250V / 11W

BASEoctal

Source datasheets

1 manufacturer datasheets cross-checked for KT63

1 verified

EXECUTIVE SUMMARY

The KT63 is a indirectly-heated beam tetrode from GEC·MOV, introduced around 1940. Commonly used in power (se) applications. British vintage pentode. Warm midrange.

HISTORY

Introduced1940ManufacturerGEC·MOV

Pre-War

KT63 Datasheet

Local mirror · PDF

↗

METRIX TESTER

Test this tube on a Metrix

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

SIMILAR TETRODES

View all →

12E1Power 1614Power (PP)1625Transmitting / Power 4Y100ROutput Power 4Y75ROutput Power 5881Power (PP)5AQ5Power 5V6Power