What is the EL51 vacuum tube?

The EL51 is a pentode vacuum tube designed for power (se/pp) applications. Big Philips power pentode. 45W capable..

What are the key specifications of the EL51?

Amplification factor μ ≈ 16, transconductance gm ≈ 11 mA/V, plate resistance rp ≈ 33.0 kΩ, max plate voltage 750 V, max plate dissipation 45 W, heater 6.3 V / 1.9 A.

Is the EL51 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the EL51 as Rare 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 EL51 sound like?

Big Philips power pentode. 45W capable.. 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.

EL51 Pentode Vacuum Tube

Power pentode delivering up to 45W in pentode, UL, or triode mode

PentodeHeater 6.3 V · 1.9 A8-pin Side Contact P8APhilips 1950

Plate dissipation: 45W
Max plate voltage: 750V
Max screen voltage: 750V
Max cathode current: 200mA
Transconductance: 11mA/V

EL51

Characteristics

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

HeaterIndirectly heated

Specifications of EL51 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.9 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of EL51 — Limiting values
Plate voltageVa max	750 V
Screen voltageVg2 max	750 V
Plate dissipationPa max	45 W
Cathode currentIk max	200 mA
Heater–cathode voltageVhk max	50 V

Mechanical

Specifications of EL51 — Mechanical
Base	8-pin Side Contact P8A
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of EL51 — Small signal
Transconductance	11 mA/V
Plate resistance	33 kΩ
Amplification factor	16

Capacitances

Specifications of EL51 — Capacitances
Input	15 pF
Grid–plate	1.5 pF
Output	8 pF

Charactereditorial reading, not a measurement

Specifications of EL51 — Character
Gain	16%
Power	100%
Drive	67%
Linearity	92%

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

Typical operation

Conditions published by the manufacturers, one row per condition. Nothing is computed.

Typical operation
Setup	Va	Ia	Source
triode connection, single-endedclass not stated	500 V	95 mA	read on the sheet TESLA · 1950 · transcript

Using this tube

Interactive loadline calculator not available for this tube yet — it needs calibrated Koren or Ayumi parameters.

Applications

Power output

Generic pentode power (se/pp) stage

PA/public address

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Philips/Mullard EL51 datasheet

Manufacturer datasheets

4 manufacturer datasheets cross-checked for EL514 verified

Triode-connectedTESLAn.d. (feuilles 3306/9306, années 1950)

Va: 500 V
Ia: 95 mA

EL51 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Philips/Mullard EL51 datasheet
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The EL51 is a indirectly-heated pentode from Philips, introduced around 1950. It provides a gain factor (μ) of 16 with 33.0kΩ plate resistance. Commonly used in power (se/pp) applications. Big Philips power pentode. 45W capable.

History

Introduced: 1950
Manufacturer: Philips
Era: Golden Age

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