What is the C3g vacuum tube?

The C3g is a pentode vacuum tube designed for preamp / driver applications. German Post legend. Ultra-linear..

What is a C3g substitute or equivalent?

Direct equivalents to the C3g include C3m. 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 C3g?

Amplification factor μ ≈ 41, transconductance gm ≈ 14 mA/V, plate resistance rp ≈ 300.0 kΩ, max plate voltage 220 V, max plate dissipation 3.5 W, heater 6.3 V / 0.37 A.

Is the C3g still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the C3g as Sought-after 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 C3g sound like?

German Post legend. Ultra-linear.. 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.

C3g Pentode Vacuum Tube

Also known as C3m

Small-signal pentode for low-noise voltage amplification

PentodeHeater 6.3 V · 0.37 A8-pin LoctalSiemens 1954

Plate dissipation: 3.5W
Max plate voltage: 220V
Amplification factor: 41
Transconductance: 14mA/V
Plate resistance: 300kΩ

C3g

Characteristics

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

HeaterIndirectly heated

Specifications of C3g — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.37 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of C3g — Limiting values
Plate voltageVa max	220 V
Screen voltageVg2 max	100 V
Plate dissipationPa max	3.5 W
Cathode currentIk max	30 mA

Mechanical

Specifications of C3g — Mechanical
Base	8-pin Loctal
Rarity	Sought-after
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of C3g — Small signal
Transconductance	14 mA/V
Plate resistance	300 kΩ
Amplification factor	41

Capacitances

Specifications of C3g — Capacitances
Input	9.5 pF
Grid–plate	0.012 pF
Output	3.5 pF

Charactereditorial reading, not a measurement

Specifications of C3g — Character
Gain	41%
Power	9%
Drive	0%
Linearity	80%

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

Using this tube

No interactive loadline model for this tube yet — download a SPICE model below to simulate it in LTspice or ngspice.

Applications

Voltage amplifier

Generic pentode preamp / driver stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : Siemens C3g datasheet (vacuumtubes.io)

Manufacturer datasheets

3 manufacturer datasheets cross-checked for C3g3 verified

Triode-connectedTelefunken010163 / 020163 / 030163 / 040163 (1963) — "Vorlaeufige technische Daten / Tentative data"

Ia: 17 mA
gm: 17 mA/V
µ: 200

C3g DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: Siemens C3g datasheet (vacuumtubes.io)
Reviewed: 2026-05-29
Status: DataModelCalc
Model: under review

Context

The C3g is a indirectly-heated pentode from Siemens, introduced around 1954. It provides a gain factor (μ) of 41 with 300.0kΩ plate resistance. Commonly used in preamp / driver applications. German Post legend. Ultra-linear.

History

Introduced: 1954
Manufacturer: Siemens
Era: Golden Age

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