What is the CK6688 vacuum tube?

The CK6688 is a pentode vacuum tube designed for preamp applications. Raytheon selected..

What is a CK6688 substitute or equivalent?

Direct equivalents to the CK6688 include 6688/E180F. 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 CK6688?

Amplification factor μ ≈ 50, transconductance gm ≈ 16.5 mA/V, plate resistance rp ≈ 90.0 kΩ, max plate voltage 210 V, max plate dissipation 3 W, heater 6.3 V / 0.3 A.

Is the CK6688 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the CK6688 as Moderate 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 CK6688 sound like?

Raytheon selected.. 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

←CK6688

← CK6336A CV1040 →Compare → 6AH6

CK6688 Pentode Vacuum Tube

Pentode6.3V / 0.3A9-pin NovalSPICE

Sourcecryptomuseum 6688.pdf (Raytheon CK6688 = E180F)Reviewed2026-05-29StatusDataModelCalcModelKoren pentodePDF

Small-signal pentode for low-noise voltage amplification

Datasheet ↗SPICE

CK6688 — Raytheon — pentode vacuum tube — (1958)

90.0kΩ

16.5mA/V

7.5pF

0.0pF

3.00pF

GAIN50%

POWER8%

DRIVE10%

LINEARITY75%

SPECIFICATIONS

Heater6.3 V · 0.3 A

Max Plate Voltage210 V

Pa max3 W

Gain Factor50

gm16.5 mA/V

rp90.0 kΩ

Inter-electrode capacitances

Cgk7.5 pF

Cgp0.03 pF

Cpk3 pF

Pinout9-pin Noval

Era1958

RarityModerate

HEATER6.3V / 0.3A

MAX PLATE210V / 3W

BASEnoval

Source datasheets

6 manufacturer datasheets cross-checked for CK6688

6 verified

Triode-connectedPhilipsDecember 1968

Specs when the screen grid (g2) is tied to the anode — the tube acts as a triode.

225

According to Philips (Data handbook, Electronic components and materials) (December 1968): « g2 connected to a »

EXECUTIVE SUMMARY

The CK6688 is a indirectly-heated pentode from Raytheon, introduced around 1958. It provides a gain factor (μ) of 50 with 90.0kΩ plate resistance. Commonly used in preamp applications. Raytheon selected.

APPLICATIONS

Voltage amplifier

Generic pentode preamp stage

VS 6AH6

μ +25%Rp -82%Pd -6%Full comparison →

HISTORY

Introduced1958ManufacturerRaytheon

Golden Age

CK6688 Datasheet

Local mirror · PDF

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METRIX TESTER

Test this tube on a Metrix

SIMILAR PENTODES

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12SJ7Preamp 307APower/Output 310APreamp 35LR6Sweep / Power 47Power/Output 4P1LPower (SET output) — DHT pentode 5639Video / wideband (power)5654RF / Preamp

Equivalents & alternatives

Direct equivalents