What is the 6550 vacuum tube?

The 6550 is a tetrode vacuum tube designed for power (pp) applications. American powerhouse..

What is a 6550 substitute or equivalent?

Direct equivalents to the 6550 include KT88. 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 6550?

Amplification factor μ ≈ 8, transconductance gm ≈ 11 mA/V, plate resistance rp ≈ 12.0 kΩ, max plate voltage 600 V, max plate dissipation 35 W, heater 6.3 V / 1.6 A.

Is the 6550 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6550 as Common 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 6550 sound like?

American powerhouse.. 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

←6550

← 6528 6688 →Compare → KT88

6550 Tetrode Vacuum Tube

Tetrode6.3V / 1.6AOctalSPICE

SourceTung-Sol·GE datasheetReviewed2026-05-29StatusDataModelCalcModelKoren v1PDF

Beam power tetrode rated at 35W for high-power output stages

Datasheet ↗SPICE

6550 — Tung-Sol·GE — tetrode vacuum tube — (1955)

12.0kΩ

11.0mA/V

14.5pF

0.8pF

11.00pF

GAIN8%

POWER88%

DRIVE88%

LINEARITY95%

SPECIFICATIONS

Heater6.3 V · 1.6 A

Max Plate Voltage600 V

Pa max35 W

Gain Factor8

gm11 mA/V

rp12.0 kΩ

Inter-electrode capacitances

Cgk14.5 pF

Cgp0.82 pF

Cpk11 pF

PinoutOctal

Era1955

RarityCommon

HEATER6.3V / 1.6A

MAX PLATE600V / 35W

BASEoctal

Source datasheets

2 manufacturer datasheets cross-checked for 6550

2 verified

EXECUTIVE SUMMARY

The 6550 is a beam power tetrode developed by Tung-Sol in 1955 specifically for high-power audio amplifier use, with a plate dissipation of 35W. It shares the KT88's octal base and general operating envelope but has a distinctly different sonic character: tighter, more controlled, and more linear than the KT88, with slightly less midrange bloom but superior bass definition. The 6550 is the original output tube of the McIntosh MC275 and many Ampeg bass amplifiers, where its clean headroom and damping characteristics are valued. Tung-Sol 6550 (original and reissue), GE 6550A, and Svetlana/SED 6550C are the notable variants.

APPLICATIONS

High-power output

Dynaco Mark IIIMcIntosh MC275SVT bass amplifier

• Guitar amp• PA/public address

VS KT88

μ 0%Rp +0%Pd -17%Full comparison →

HISTORY

Introduced1955ManufacturerTung-Sol·GE

Golden Age