What is a 4P1L substitute or equivalent?

Direct equivalents to the 4P1L include None standard (Soviet DHT pentode for low-voltage portable / battery service). 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 4P1L?

Transconductance gm ≈ 5 mA/V, max plate voltage 200 V, max plate dissipation 7 W, heater 2.1 V / 0.65 A.

Is the 4P1L still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 4P1L 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.

By Jean-Michel Falligan Devergne · Reviewed May 9, 2026

←4P1L

← 47 4Y100R →Compare…

4P1L 4P1L / 4П1Л Pentode Vacuum Tube

Q: What is the 4P1L vacuum tube?

The 4P1L (4P1L / 4П1Л) is a pentode vacuum tube designed for power (set output) — dht pentode applications. Soviet directly-heated power pentode in 8-pin Loctal envelope. Originally designed for low-voltage portable / battery-powered military gear; rediscovered by SET amplifier builders in the 2010s for its DHT character at modest plate voltages. Filament: 2.1V × 0.65A (series-connected) or 4.2V × 0.325A (parallel) — both modes produce identical plate curves..

Pentode2.1V / 0.65A8-pin LoctalSPICE

SourceRussian 4П1Л datasheet · external audit feedbackReviewed2026-05-09StatusDataModelCalcModelKoren pentodePDF

Small-signal pentode for low-noise voltage amplification

Datasheet ↗SPICE

4P1L / 4П1Л — Russian — pentode vacuum tube — (1955)

5.0mA/V

8.5pF

0.0pF

4.50pF

GAIN0%

POWER18%

DRIVE50%

LINEARITY75%

SPECIFICATIONS

Heater2.1 V · 0.65 A

Max Plate Voltage200 V

Pa max7 W

Gain Factor—

gm5 mA/V

rp—

Inter-electrode capacitances

Cgk8.5 pF

Cgp0.02 pF

Cpk4.5 pF

Pinout8-pin Loctal

Era1955

RarityModerate

HEATER2.1V / 0.65A

MAX PLATE200V / 7W

BASEloctal

EXECUTIVE SUMMARY

The 4P1L is a directly-heated pentode from Russian, introduced around 1955. Commonly used in power (set output) — dht pentode applications. Soviet directly-heated power pentode in 8-pin Loctal envelope. Originally designed for low-voltage portable / battery-powered military gear; rediscovered by SET amplifier builders in the 2010s for its DHT character at modest plate voltages. Filament: 2.1V × 0.65A (series-connected) or 4.2V × 0.325A (parallel) — both modes produce identical plate curves.

HISTORY

Introduced1955ManufacturerRussian

Golden Age

4P1L Datasheet

Frank's Electron Tube Pages · PDF

↗

METRIX TESTER

Test this tube on a Metrix

SIMILAR PENTODES

View all →

12SJ7Preamp 307APower/Output 310APreamp 35LR6Sweep / Power 47Power/Output 5639Video / wideband (power)5654RF / Preamp 5902Power (output)