What is the 6BL7 vacuum tube?

The 6BL7 (6BL7GT) is a triode vacuum tube designed for driver applications. Medium mu twin triode. Punchy driver..

What is a 6BL7 substitute or equivalent?

Direct equivalents to the 6BL7 include 6BL7GTA. 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 6BL7?

Amplification factor μ ≈ 15, transconductance gm ≈ 7 mA/V, plate resistance rp ≈ 2.1 kΩ, max plate voltage 500 V, max plate dissipation 10 W, heater 6.3 V / 1.5 A.

Is the 6BL7 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6BL7 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 6BL7 sound like?

Medium mu twin triode. Punchy driver.. 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.

6BL7 GT Triode Vacuum Tube

Also known as 6BL7GTA

Power triode delivering 10W for push-pull and SET designs

Dual triodeHeater 6.3 V · 1.5 AOctal2 sectionsRCA·GE·Sylvania 1952

Plate dissipation: 10W
Max plate voltage: 500V
Transconductance: 7mA/V

6BL7

Characteristics

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

HeaterIndirectly heated

Specifications of 6BL7 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.5 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6BL7 — Limiting values
Plate voltageVa max	500 V
Plate dissipationPa max	10 W
Heater–cathode voltageVhk max	200 V

Mechanical

Specifications of 6BL7 — Mechanical
Base	Octal
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6BL7 — Small signal
Transconductance	7 mA/V
Plate resistance	2.1 kΩ
Amplification factor	15

Capacitances

Specifications of 6BL7 — Capacitances
Grid–cathode	4.2 pF
Grid–plate	6 pF
Plate–cathode	0.9 pF

Charactereditorial reading, not a measurement

Specifications of 6BL7 — Character
Gain	15%
Power	25%
Drive	98%
Linearity	93%

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	Vg1 / Rk	Ia	gm	μ	rp	Source
Class A, single-endedtriode connection · fixed bias	250 V	-9 V	40 mA		15	2.1 kΩ	OCR, to be checked RCA · 1953 · p. 1 · transcript
triode connection, single-endedclass not stated · fixed bias	250 V	-9 V	40 mA	7 mA/V	15		OCR, to be checked General Electric · 1957 · p. 2 · transcript

Model at this condition: Ayumi Nakabayashi Model
μ: 16.2
gm: 7.31 mA/V
rp: 2.2 kΩ

Using this tube

Applications

SET output
Push-pull output
Phase splitter

Generic triode driver stage

Headphone amp

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Active model : Ayumi Nakabayashi

Manufacturer datasheets

5 manufacturer datasheets cross-checked for 6BL7GT5 verified

6BL7 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·GE·Sylvania
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi

Context

The 6BL7 is a dual indirectly-heated triode from RCA·GE·Sylvania, introduced around 1952. It provides a gain factor (μ) of 15 with 2150Ω plate resistance. Commonly used in driver applications. Medium mu twin triode. Punchy driver.

History

Introduced: 1952
Manufacturer: RCA·GE·Sylvania
Era: Golden Age

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