What is the 6BK5 vacuum tube?

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

What is a 6BK5 substitute or equivalent?

Direct equivalents to the 6BK5 include None. 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 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.

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

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6BK5 Tetrode Vacuum Tube

Tetrode6.3V / 1.2AOctalSPICE

SourceRadiomuseum 6BK5 datasheetReviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

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

Datasheet ↗SPICE

6BK5 — RCA — tetrode vacuum tube — (1952)

100.0kΩ

8.5mA/V

13.0pF

0.1pF

5.00pF

GAIN0%

POWER23%

DRIVE0%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 1.2 A

Max Plate Voltage250 V

Pa max9 W

Gain Factor—

gm8.5 mA/V

rp100.0 kΩ

Inter-electrode capacitances

Cgk13 pF

Cgp0.06 pF

Cpk5 pF

PinoutOctal

Era1952

RarityCommon

HEATER6.3V / 1.2A

MAX PLATE250V / 9W

BASEnoval

Source datasheets

2 manufacturer datasheets cross-checked for 6BK5

2 verified

EXECUTIVE SUMMARY

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

HISTORY

Introduced1952ManufacturerRCA

Golden Age

6BK5 Datasheet

Local mirror · PDF

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METRIX TESTER

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