What is the 6688 vacuum tube?

The 6688 is a pentode vacuum tube designed for preamp applications. Selected pentode..

What is a 6688 substitute or equivalent?

Direct equivalents to the 6688 include CK6688. 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 6688?

Transconductance gm ≈ 16.5 mA/V, plate resistance rp ≈ 90.0 kΩ, max plate voltage 210 V, max plate dissipation 2.7 W, heater 6.3 V / 0.3 A.

Is the 6688 still in production?

Production status varies by year and manufacturer. The current Amperatubes catalog classifies the 6688 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 6688 sound like?

Selected pentode.. 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.