What is the EF804S vacuum tube?

The EF804S is a pentode vacuum tube designed for preamp / microphone applications. Telefunken diamond. V72 preamp legend..

What are the key specifications of the EF804S?

Amplification factor μ ≈ 38, transconductance gm ≈ 2 mA/V, plate resistance rp ≈ 2000.0 kΩ, max plate voltage 300 V, max plate dissipation 1 W, heater 6.3 V / 0.17 A.

Is the EF804S still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the EF804S as Collector 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 EF804S sound like?

Telefunken diamond. V72 preamp legend.. 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.

EF804S Pentode Vacuum Tube

Small-signal pentode for low-noise voltage amplification

PentodeHeater 6.3 V · 0.17 A9-pin NovalTelefunken 1951

Plate dissipation: 1W
Max plate voltage: 300V
Amplification factor: 38
Transconductance: 2mA/V
Plate resistance: 2MΩ

EF804S

Characteristics

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

HeaterIndirectly heated

Specifications of EF804S — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.17 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of EF804S — Limiting values
Plate voltageVa max	300 V
Screen voltageVg2 max	200 V
Plate dissipationPa max	1 W
Screen dissipationPg2 max	0.2 W
Cathode currentIk max	6 mA
Grid resistorRg1 max	3 MΩ
Peak plate voltageVao	550 V
Heater–cathode voltageVhk max	100 V

Mechanical

Specifications of EF804S — Mechanical
Base	9-pin Noval
Rarity	Collector
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of EF804S — Small signal
Transconductance	2 mA/V
Plate resistance	2 MΩ
Amplification factor	38

Capacitances

Specifications of EF804S — Capacitances
Input	4.3 pF
Grid–plate	0.06 pF
Output	5.5 pF

Charactereditorial reading, not a measurement

Specifications of EF804S — Character
Gain	38%
Power	3%
Drive	0%
Linearity	81%

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

Using this tube

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

Applications

Voltage amplifier

Generic pentode preamp / microphone stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026

Manufacturer datasheets

2 manufacturer datasheets cross-checked for EF804S2 verified

EF804S DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

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

Context

The EF804S is a indirectly-heated pentode from Telefunken, introduced around 1951. It provides a gain factor (μ) of 38 with 2000.0kΩ plate resistance. Commonly used in preamp / microphone applications. Telefunken diamond. V72 preamp legend.

History

Introduced: 1951
Manufacturer: Telefunken
Era: Golden Age

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