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.

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..

Small-signal pentode for low-noise voltage amplification

PentodeHeater 2.1 V · 0.65 A8-pin LoctalRussian 1955

Plate dissipation: 7W
Max plate voltage: 200V
Transconductance: 5mA/V

4P1L

Characteristics

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

HeaterDirectly heated

Specifications of 4P1L — Heater
Heater voltageVh	2.1 V
Heater currentIh	0.65 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of 4P1L — Limiting values
Plate voltageVa max	200 V
Plate dissipationPa max	7 W

Mechanical

Specifications of 4P1L — Mechanical
Base	8-pin Loctal
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of 4P1L — Small signal
Transconductance	5 mA/V

Capacitances

Specifications of 4P1L — Capacitances
Input	8.5 pF
Grid–plate	0.02 pF
Output	4.5 pF

Charactereditorial reading, not a measurement

Specifications of 4P1L — Character
Gain	0%
Power	18%
Drive	50%
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 9, 2026Source : Russian 4П1Л datasheet · external audit feedbackActive model : Koren pentode

Manufacturer datasheets

4P1L DatasheetFrank's Electron Tube Pages · PDF

SPICE models

Revision and verification status

Source: Russian 4П1Л datasheet · external audit feedback
Reviewed: 2026-05-09
Status: DataModelCalc
Model: Koren pentode

Context

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

Introduced: 1955
Manufacturer: Russian
Era: Golden Age

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