What is the 6SL7 vacuum tube?

The 6SL7 (6SL7GT) is a triode vacuum tube designed for preamp applications. Silky, dark..

What is a 6SL7 substitute or equivalent?

Direct equivalents to the 6SL7 include 5691, CV1985. 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 6SL7?

Amplification factor μ ≈ 70, transconductance gm ≈ 1.6 mA/V, plate resistance rp ≈ 44.0 kΩ, max plate voltage 275 V, max plate dissipation 1.1 W, heater 6.3 V / 0.3 A.

Is the 6SL7 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6SL7 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 6SL7 sound like?

Silky, dark.. 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.

6SL7 GT Triode Vacuum Tube

Also known as 5691 · CV1985

Medium-gain triode for voltage amplification applications

Dual triodeHeater 6.3 V · 0.3 AOctal2 sectionsRCA·Sylvania 1941

Plate dissipation: 1.1W
Max plate voltage: 275V
Amplification factor: 70
Transconductance: 1.6mA/V
Plate resistance: 44kΩ

6SL7

Characteristics

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

HeaterIndirectly heated

Specifications of 6SL7 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6SL7 — Limiting values
Plate voltageVa max	275 V
Plate dissipationPa max	1.1 W
Heater–cathode voltageVhk max	100 V

Mechanical

Specifications of 6SL7 — Mechanical
Base	Octal
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6SL7 — Small signal
Transconductance	1.6 mA/V
Plate resistance	44 kΩ
Amplification factor	70

Capacitances

Specifications of 6SL7 — Capacitances
Grid–cathode	1.5 pF
Grid–plate	1.5 pF
Plate–cathode	2 pF

Charactereditorial reading, not a measurement

Specifications of 6SL7 — Character
Gain	70%
Power	3%
Drive	56%
Linearity	65%

datasheet cited · model or editorial reading · catalogue value, no citation attached yet · nothing invented

Typical operation

Canonical operating pointSPICE model2 availableModel

B+: 365 V
Load: 50 kΩ
Va: 219 V
Ia: 1.5 mA
Vg: -2 V
Pd: 0.33 W
Gain: 31.1 dB

At Q: Ayumi Nakabayashi · 2 engines
μ: 67.6
gm: 1.42 mA/V
rp: 47.7 kΩ

Design a stage →

Using this tube

Applications

Voltage amplifier
High-gain preamp
Phase splitter

RCA BA-1A preamp

Hi-Fi stereoHeadphone ampStudio/recording

Classic circuits

6SL7 Driver Stage
Preamp Stage
6SL7 high-mu octal triode as voltage amplifier. The octal predecessor to the 12AX7. Used extensively in 1940s-50s hi-fi preamps.
SEVb 250V · Vg -2V · RL 220kΩRCA 6SL7GT Datasheet

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : RCA·Sylvania datasheetActive model : Ayumi Nakabayashi · 2 engines

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 6SL7GT1 verified

6SL7 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: RCA·Sylvania datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Ayumi Nakabayashi · 2 engines

Context

The 6SL7 is the high-mu (mu ~70) companion to the 6SN7, sharing the same octal envelope but with higher gain and higher plate resistance (~44k ohms). It was widely used as a voltage amplifier and phase inverter in 1940s-50s amplifiers and fills a role similar to the 12AX7 but with the sonic advantages of the larger octal bottle construction. Its higher plate resistance compared to the 6SN7 makes it less suitable for driving loads but excellent as a first-stage gain element. RCA grey-glass and Sylvania versions are well-regarded NOS options, though availability has become increasingly scarce.

History

Introduced: 1941
Manufacturer: RCA·Sylvania
Era: Pre-War

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