What is the 6BK5 vacuum tube?

The 6BK5 is a tetrode vacuum tube designed for power applications. Audio output pentode..

What are the key specifications of the 6BK5?

Transconductance gm ≈ 8.5 mA/V, plate resistance rp ≈ 100.0 kΩ, max plate voltage 250 V, max plate dissipation 9 W, heater 6.3 V / 1.2 A.

Is the 6BK5 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6BK5 as Common 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 6BK5 sound like?

Audio output pentode.. 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.

6BK5 Tetrode Vacuum Tube

Beam power tetrode rated at 9W for high-power output stages

TetrodeHeater 6.3 V · 1.2 AOctalRCA 1952

Plate dissipation: 9W
Max plate voltage: 250V
Transconductance: 8.5mA/V

6BK5

Characteristics

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

HeaterIndirectly heated

Specifications of 6BK5 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.2 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6BK5 — Limiting values
Plate voltageVa max	250 V
Plate dissipationPa max	9 W

Mechanical

Specifications of 6BK5 — Mechanical
Base	Octal
Rarity	Common
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6BK5 — Small signal
Transconductance	8.5 mA/V
Plate resistance	100 kΩ

Capacitances

Specifications of 6BK5 — Capacitances
Input	13 pF
Grid–plate	0.06 pF
Output	5 pF

Charactereditorial reading, not a measurement

Specifications of 6BK5 — Character
Gain	0%
Power	23%
Drive	0%
Linearity	75%

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	Va	Vg2	Vg1 / Rk	Ia	Ig2	Load	Pout	gm	rp	Source
Class A, single-endedpentode connection · fixed bias	250 V	250 V	-5 V	35 mA	3.5 mA	6.5 kΩ	3.5 W	8.5 mA/V	100 kΩ	OCR, to be checked Tung-Sol · 1957 · p. 2 · transcript

Using this tube

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Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Radiomuseum 6BK5 datasheetActive model : Koren pentode

Manufacturer datasheets

2 manufacturer datasheets cross-checked for 6BK52 verified

6BK5 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Radiomuseum 6BK5 datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren pentode

Context

The 6BK5 is a indirectly-heated beam tetrode from RCA, introduced around 1952. Commonly used in power applications. Audio output pentode.

History

Introduced: 1952
Manufacturer: RCA
Era: Golden Age

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