What is a 6P31S substitute or equivalent?

Direct equivalents to the 6P31S include EL36 / 6CM5 / 6G-B7 (line-scan beam tetrode); NOT pin-compatible with EL84. 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 6P31S?

Transconductance gm ≈ 12.5 mA/V, plate resistance rp ≈ 4.0 kΩ, max plate voltage 300 V, max plate dissipation 10 W, heater 6.3 V / 1.3 A.

Is the 6P31S still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6P31S 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 6P31S sound like?

Russian line-scan output tube related to EL36 / 6CM5 class; not EL84-compatible.. 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.

6P31S Tetrode Vacuum Tube

Q: What is the 6P31S vacuum tube?

The 6P31S is a tetrode vacuum tube designed for power applications. Russian line-scan output tube related to EL36 / 6CM5 class; not EL84-compatible..

Also known as EL36 · 6CM5 · 6G-B7 (line-scan beam tetrode) · NOT pin-compatible with EL84

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

TetrodeHeater 6.3 V · 1.3 A9-pin NovalRussian 1965

Plate dissipation: 10W
Max plate voltage: 300V
Max screen voltage: 170V
Transconductance: 12.5mA/V

6P31S

Characteristics

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

HeaterIndirectly heated

Specifications of 6P31S — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 6P31S — Limiting values
Plate voltageVa max	300 V
Screen voltageVg2 max	170 V
Plate dissipationPa max	10 W

Mechanical

Specifications of 6P31S — Mechanical
Base	9-pin Noval
Rarity	Common
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 6P31S — Small signal
Transconductance	12.5 mA/V
Plate resistance	4 kΩ

Capacitances

Specifications of 6P31S — Capacitances
Input	18 pF
Grid–plate	1.3 pF
Output	8.5 pF

Charactereditorial reading, not a measurement

Specifications of 6P31S — Character
Gain	0%
Power	25%
Drive	96%
Linearity	75%

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

Using this tube

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Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Russian 6П31С datasheet · wording corrected: not EL84-compatibleActive model : Koren pentode

Manufacturer datasheets

1 manufacturer datasheets cross-checked for 6P31S1 verified

6P31S DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Russian 6П31С datasheet · wording corrected: not EL84-compatible
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren pentode

Context

The 6P31S is a indirectly-heated beam tetrode from Russian, introduced around 1965. Commonly used in power applications. Russian line-scan output tube related to EL36 / 6CM5 class; not EL84-compatible.

History

Introduced: 1965
Manufacturer: Russian
Era: Late Production

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