Can I swap a 6L6GC for a 5881?

They share a base and envelope so they fit the same socket, but the operating point differs — expect to re-set the bias rather than perform a blind drop-in.

What is the difference between the 6L6GC and the 5881?

The 6L6GC has μ≈8 with about 30 W maximum plate dissipation; the 5881 has μ≈8 with about 23 W. The higher μ is on the 6L6GC, the higher plate dissipation rating on the 6L6GC.

Which is better, the 6L6GC or the 5881?

Neither is universally better — it depends on the circuit and the tone you want in a guitar amp. Compare the side-by-side specifications and the comparison by objective on this page (gain, load, current, dissipation margin, heater, base) to choose for your build.

6L6GC vs 5881

6L6GC versus 5881 / 6L6WGB — two tetrodes compared.

6L6GC vs 5881: what differs

The 6L6GC and 5881 share a family but trade gain for headroom: 5881 has the higher amplification factor (μ ≈ 8), making it the typical choice for high-gain preamp stages. 6L6GC runs lower μ (8) and is the standard cathode follower / phase-splitter / line-stage triode. They share the same envelope and base — wire them in the same socket and only the operating point changes.

Comparison by objective

Choose what the stage has to do: the quantities below are reordered and weighted for that objective. Every value comes from the catalogue and from the datasheet typical operating point; a missing value shows “—” with its reason. No score, no ranking — only measured differences.

Voltage amplification of a small signal — common cathode with a resistive plate load.

Quantity

6L6GC

5881

Difference

Available gain (μ)Weight 3/3 · decisiveμ is the ceiling of the voltage gain of a common-cathode stage.Av ≈ μ · Ra / (Ra + rp) — with Ra = 2–3 × rp the stage reaches about 2/3 to 3/4 of μ. As a follower the gain is close to 1 whatever μ.

6L6GC

5881

Differenceidentical

Load to drive (rp)Weight 2/3 · importantPlate resistance: the lower rp, the lower the load the stage can drive at the same gain and linearity.Ra ≥ 2–3 × rp for a common-cathode stage. As a cathode follower the output impedance is about 1 / gm.

6L6GC

22.5 kΩRa ≥ 45 kΩ – 67.5 kΩ

5881

30 kΩRa ≥ 60 kΩ – 90 kΩ

Differenceratio ×1.3

Available current (Ia typical)Weight 1/3 · to checkPlate current at the datasheet typical operating point — what the stage can deliver into a capacitance or a low load.Read from the published typical point (Va, Vg). No operating point is derived from a model here.

6L6GC

72 mAat Va 250 V, Vg −14 VTypical point: RCA (Radio Corporation of America), Electron Tube Division, Harrison NJ · 8-60 (août 1960)

5881

75 mAat Va 250 V, Vg −14 VTypical point: RCA (Radio Corporation of America, Harrison, New Jersey) · 1957 (2-57, TENTATIVE DATA)

Differenceratio ×1

Dissipation margin (Pa max − Pd typical)Weight 1/3 · to checkDifference between the maximum plate dissipation and the dissipation at the typical point (Pd = Va · Ia).Pd at idle < 70 % of Pa max.

6L6GC

12 WPa max 30 W · Pd typical 18 W (60 % of Pa max)Typical point: RCA (Radio Corporation of America), Electron Tube Division, Harrison NJ · 8-60 (août 1960)

5881

4.25 WPa max 23 W · Pd typical 18.75 W (82 % of Pa max)Typical point: RCA (Radio Corporation of America, Harrison, New Jersey) · 1957 (2-57, TENTATIVE DATA)

Differencedifference −7.75 W

Heater (V × A)Weight 1/3 · to checkHeater voltage and current, hence the power drawn from the heater winding.Same voltage required; the winding must supply the summed current of the tubes in parallel (or the same current in series).

6L6GC

5.7 W6.3 V × 0.9 A

5881

5.7 W6.3 V × 0.9 A

Differenceidentical

Base compatibilityWeight 1/3 · to checkBase and pin-by-pin function according to the catalogue pinouts.Same base and identical pinout → same socket. Same base, different pins → rewiring. Different base → adapter or new socket.

6L6GC

octalOctal · 8 pins

5881

octalOctal · 8 pins

Differencesame base, identical pinout

Rules: Amplifier topologies guide, §07 “Design rules of thumb”

Physical compatibility

6L6GC

5881

Base

octal

Pinout

Octal

identical pin by pin (8 pins)

Sections

Bulb diameter (max)

—

— no mechanical data in the catalogue

Heating

6L6GC

5881

Heating

Indirect (IHT)

Heater voltage

6.3 V

same voltage — the same winding can feed both · 6L6GC: no center tap · 5881: no center tap

Heater current

0.9 A

same current

Heater power

5.67 W

Bias

Datasheet typical operating point (one per tube, SEQ-02) and the cathode resistor it implies.

6L6GC

5881

Va typical

250 V

Vg typical

−14 V

Ia typical

72 mA

75 mA

Indicative Rk = |Vg| / Ia

194 Ω

187 Ω

Pd typical = Va · Ia

18 W

18.75 W

6L6GC — Typical point: RCA (Radio Corporation of America), Electron Tube Division, Harrison NJ · 8-60 (août 1960) · 5881 — Typical point: RCA (Radio Corporation of America, Harrison, New Jersey) · 1957 (2-57, TENTATIVE DATA)

Performance for the objective

Catalogue values, weighted as in the objective table (Gain input stage). rp is a design parameter, not a merit.

6L6GC

5881

Difference

identical

6 mA/V

6.1 mA/V

ratio ×1

22.5 kΩ

30 kΩ

ratio ×1.3

Pa max

30 W

23 W

difference −7 W

Va max

500 V

400 V

difference −100 V

Substitution possible under conditions

6L6GC and 5881 list each other as equivalents in the catalogue.

Substitutes for 6L6GC Substitutes for 5881

Side-by-side specifications

Side-by-side specifications of 6L6GC and 5881
Spec	6L6GC	5881
Full name	6L6GC	5881 / 6L6WGB
Type	Tetrode	Tetrode
Primary use	Power (PP)	Power (PP)
Era	1958	1952
Heating	indirect	indirect
Heater voltage	6.3 V	6.3 V
Heater current	0.9 A	0.9 A
Amplification factor (μ)	8	8
Transconductance (gm)	6 mA/V	6.1 mA/V
Plate resistance (rp)	22.5 kΩ	30 kΩ
Max plate voltage	500 V	400 V
Max plate dissipation	30 W	23 W
Base	octal	octal
Manufacturer	GE·Sylvania·RCA	Tung-Sol
Rarity	Common	Common

Sonic character

Listening folklore — not electrical data

6L6GC

American workhorse.

5881

Ruggedized 6L6.

Need an interactive deep dive?

The Amperatubes comparator visualises loadlines for both tubes side-by-side, simulates the SPICE response, and lets you adjust the operating point in real time.

Open 6L6GC vs 5881 in the interactive comparator →

6L6GC vs 5881

6L6GC vs 5881: what differs

Comparison by objective

Physical compatibility

Heating

Bias

Performance for the objective

Substitution possible under conditions

Side-by-side specifications

Sonic character

Need an interactive deep dive?

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