What is the EL37 vacuum tube?

The EL37 is a pentode vacuum tube designed for power (pp) applications. Mullard flagship pentode. Massive gm..

What is a EL37 substitute or equivalent?

Direct equivalents to the EL37 include CV586. 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 EL37?

Amplification factor μ ≈ 10, transconductance gm ≈ 11 mA/V, plate resistance rp ≈ 13.5 kΩ, max plate voltage 400 V, max plate dissipation 25 W, heater 6.3 V / 1.4 A.

Is the EL37 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the EL37 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 EL37 sound like?

Mullard flagship pentode. Massive gm.. 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.

EL37 Pentode Vacuum Tube

Also known as CV586

Power pentode delivering up to 25W in pentode, UL, or triode mode

PentodeHeater 6.3 V · 1.4 AOctalMullard 1946

Plate dissipation: 25W
Max plate voltage: 400V
Max screen voltage: 400V
Max cathode current: 200mA
Transconductance: 11mA/V

EL37

Characteristics

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

HeaterIndirectly heated

Specifications of EL37 — Heater
Heater voltageVh	6.3 V
Heater currentIh	1.4 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of EL37 — Limiting values
Plate voltageVa max	400 V
Screen voltageVg2 max	400 V
Plate dissipationPa max	25 W
Screen dissipationPg2 max	6 W
Cathode currentIk max	200 mA

Mechanical

Specifications of EL37 — Mechanical
Base	Octal
Rarity	Rare
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of EL37 — Small signal
Transconductance	11 mA/V
Plate resistance	13.5 kΩ
Amplification factor	10

Capacitances

Specifications of EL37 — Capacitances
Input	17.5 pF
Grid–plate	1 pF
Output	9 pF

Charactereditorial reading, not a measurement

Specifications of EL37 — Character
Gain	10%
Power	63%
Drive	87%
Linearity	95%

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	Vg2	Vg1 / Rk	Ia	Ig2	Load	Pout	THD	gm	rp	Source
pentode connection, push-pullclass not stated	250 V	250 V	-13.5 V	100 mA	13.5 mA	2.5 kΩ a-a	11.5 W	13.5%	11 mA/V	13.5 kΩ	OCR, to be checked Mullard · ISSUE 4 (codes 157/473/858) · p. 1 · 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 (pp) stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

2 manufacturer datasheets cross-checked for EL372 verified

EL37 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Mullard
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The EL37 is a indirectly-heated pentode from Mullard, introduced around 1946. It provides a gain factor (μ) of 10 with 13.5kΩ plate resistance. Commonly used in power (pp) applications. Mullard flagship pentode. Massive gm.

History

Introduced: 1946
Manufacturer: Mullard
Era: Golden Age

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