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.

CK6688 Pentode Vacuum Tube

Also known as 6688 · E180F

Small-signal pentode for low-noise voltage amplification

PentodeHeater 6.3 V · 0.3 A9-pin NovalRaytheon 1958

Plate dissipation: 3W
Max plate voltage: 210V
Amplification factor: 50
Transconductance: 16.5mA/V
Plate resistance: 90kΩ

CK6688

Characteristics

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

HeaterIndirectly heated

Specifications of CK6688 — Heater
Heater voltageVh	6.3 V
Heater currentIh	0.3 A

Limiting valuesDatasheet maximum ratings — not to be exceeded

Specifications of CK6688 — Limiting values
Plate voltageVa max	210 V
Screen voltageVg2 max	175 V
Plate dissipationPa max	3 W
Screen dissipationPg2 max	0.9 W
Cathode currentIk max	25 mA
Grid resistorRg1 max	250 kΩ
Peak plate voltageVao	400 V

Mechanical

Specifications of CK6688 — Mechanical
Base	9-pin Noval
Rarity	Moderate
Pinout

Small signalDatasheet parameters at the reference operating point — not limits

Specifications of CK6688 — Small signal
Transconductance	16.5 mA/V
Plate resistance	90 kΩ
Amplification factor	50

Capacitances

Specifications of CK6688 — Capacitances
Input	7.5 pF
Grid–plate	0.03 pF
Output	3 pF

Charactereditorial reading, not a measurement

Specifications of CK6688 — Character
Gain	50%
Power	8%
Drive	10%
Linearity	75%

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

Using this tube

Applications

Voltage amplifier

Generic pentode preamp stage

Replace or compare

Sources

By Jean-Michel Falligan DevergneReviewed May 29, 2026Source : cryptomuseum 6688.pdf (Raytheon CK6688 = E180F)Active model : Koren pentode

Manufacturer datasheets

6 manufacturer datasheets cross-checked for CK66886 verified

Triode-connectedPhilipsDecember 1968

µ: 225

CK6688 DatasheetLocal mirror · PDF

SPICE models

Revision and verification status

Source: cryptomuseum 6688.pdf (Raytheon CK6688 = E180F)
Reviewed: 2026-05-29
Status: DataModelCalc
Model: Koren pentode

Context

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.

History

Introduced: 1958
Manufacturer: Raytheon
Era: Golden Age

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