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.

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

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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..

Tetrode6.3V / 1.3A9-pin NovalSPICE

SourceRussian 6П31С datasheet · wording corrected: not EL84-compatibleReviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

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

Datasheet ↗SPICE

6P31S — Russian — tetrode vacuum tube — (1965)

4.0kΩ

12.5mA/V

18.0pF

1.3pF

8.50pF

GAIN0%

POWER25%

DRIVE96%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 1.3 A

Max Plate Voltage300 V

Pa max10 W

Gain Factor—

gm12.5 mA/V

rp4.0 kΩ

Inter-electrode capacitances

Cgk18 pF

Cgp1.3 pF

Cpk8.5 pF

Pinout9-pin Noval

Era1965

RarityCommon

HEATER6.3V / 1.3A

MAX PLATE300V / 10W

BASEnoval

Source datasheets

1 manufacturer datasheets cross-checked for 6P31S

1 verified

EXECUTIVE SUMMARY

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

Introduced1965ManufacturerRussian

Late Production

6P31S Datasheet

Frank's Electron Tube Pages · PDF

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