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 is a EL51 substitute or equivalent?

Direct equivalents to the EL51 include None direct. 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 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.

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

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EL51 Pentode Vacuum Tube

Pentode6.3V / 1.9A8-pin Side Contact P8A

SourcePhilips/Mullard EL51 datasheetReviewed2026-05-29StatusDataModelCalcModelunder reviewPDF

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

Datasheet ↗

EL51 — Philips — pentode vacuum tube — (1950)

33.0kΩ

11.0mA/V

15.0pF

1.5pF

8.00pF

GAIN16%

POWER100%

DRIVE67%

LINEARITY92%

SPECIFICATIONS

Heater6.3 V · 1.9 A

Max Plate Voltage750 V

Pa max45 W

Gain Factor16

gm11 mA/V

rp33.0 kΩ

Inter-electrode capacitances

Cgk15 pF

Cgp1.5 pF

Cpk8 pF

Pinout8-pin Side Contact P8A

Era1950

RarityRare

HEATER6.3V / 1.9A

MAX PLATE750V / 45W

BASEp8a-sc

Source datasheets

4 manufacturer datasheets cross-checked for EL51

4 verified

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

Specs when the screen grid (g2) is tied to the anode — the tube acts as a triode.

500 V

95 mA

According to TESLA (Tchécoslovaquie) (n.d. (feuilles 3306/9306, années 1950)): « triode connection »

EXECUTIVE SUMMARY

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.

APPLICATIONS

Power output

Generic pentode power (se/pp) stage

• PA/public address

HISTORY

Introduced1950ManufacturerPhilips

Golden Age

EL51 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.

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