What is the KT61 vacuum tube?

The KT61 is a tetrode vacuum tube designed for power (se) applications. British beam tetrode. Smooth, refined..

What is a KT61 substitute or equivalent?

Direct equivalents to the KT61 include 6P25, CV1853. 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 KT61?

Amplification factor μ ≈ 27, transconductance gm ≈ 10.5 mA/V, plate resistance rp ≈ 2.8 kΩ, max plate voltage 275 V, max plate dissipation 10 W, heater 6.3 V / 0.95 A.

Is the KT61 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the KT61 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 KT61 sound like?

British beam tetrode. Smooth, refined.. 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

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KT61 Tetrode Vacuum Tube

Tetrode6.3V / 0.95AOctal

SourceGEC·MOVReviewed—StatusDataModelCalcModelunder reviewPDF

Beam power tetrode rated at 10W for high-power output stages

Datasheet ↗

KT61 — GEC·MOV — tetrode vacuum tube — (1940)

2.8kΩ

10.5mA/V

9.0pF

0.3pF

8.50pF

GAIN27%

POWER25%

DRIVE97%

LINEARITY87%

SPECIFICATIONS

Heater6.3 V · 0.95 A

Max Plate Voltage275 V

Pa max10 W

Gain Factor27

gm10.5 mA/V

rp2.8 kΩ

Inter-electrode capacitances

Cgk9 pF

Cgp0.3 pF

Cpk8.5 pF

PinoutOctal

Era1940

RaritySought-after

HEATER6.3V / 0.95A

MAX PLATE275V / 10W

BASEoctal

EXECUTIVE SUMMARY

The KT61 is a indirectly-heated beam tetrode from GEC·MOV, introduced around 1940. It provides a gain factor (μ) of 27 with 2750Ω plate resistance. Commonly used in power (se) applications. British beam tetrode. Smooth, refined.

HISTORY

Introduced1940ManufacturerGEC·MOV

Pre-War

KT61 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

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

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