STC CV391 (5B/255M) Vacuum Tube
What is Archive Tubes?
Archive Tubes is a new brand built around the preserved stock of a long-established tube purveyor that’s been cataloging NOS (New Old Stock, unused vintage) inventory for generations. They're bringing properly tested, warranted, and trustworthy vintage tubes to audiophiles who are tired of gambling on mystery sellers.
How Archive Tubes are Graded
Vacuum tubes were hand-made for decades, so the two triodes inside them were never perfectly identical. We match them today so you get predictable performance in audio circuits.
- Archive Vault: Triodes match within 5%
- Gold: Triodes match within 6-10%
- Silver: Triodes match within 11–20%
Archive Tubes Warranty
All Archive Tubes sold by Apos include a one-year warranty. This warranty covers manufacturing defects for twelve months from the date of purchase.
Warranty Details
Archive Assessed, Apos Assured
All Archive tubes are thoroughly tested, inspected, photographed, and inventoried, guaranteeing the quality of each tube that's shipped to customers. All tubes carry an Apos 12-month warranty against manufacturing defects.
Are the tubes...dusty...?
Because these are genuine New Old Stock tubes, small cosmetic irregularities may be present. These aren't defects but artifacts of vintage manufacturing and decades of storage. They have no impact on reliability or sonic performance.
Specs
- Brand / Type: STC CV391 (5B/255M)
- Military Grade: Yes
- Made in: UK
- Box Type: NOS in New Box
- Tested on: Amplitrex AT1000 Advanced Digital Tube Tester
What's a tube plate?
The plate, or anode, is the metal inside a vacuum tube that collects electrons and shapes the signal. Its size, material, and design affect tone, dynamics, and how the tube handles heat and vibration. Differences like black vs. grey or long vs. short plates affect warmth, clarity, and reliability.
Learn more about Tube Plates & Types
What’s a tube getter?
The getter is a reactive metal inside a vacuum tube that absorbs leftover gases and keeps the vacuum stable. Its shape and placement—ring, D, O, halo, or disc—affect how the tube handles noise, microphonics, and long-term reliability. Beyond function, getter design also reveals a tube’s era, origin, and the sonic priorities of the factory that made it.
Learn more about Tube Getters & Types
What’s a JAN or Military-Spec Tube?
Originally built for wartime reliability, JAN and military-spec tubes were engineered to survive heat, vibration, and constant use in radios and radar. Made under strict Joint Army–Navy standards, they feature thicker glass, reinforced micas, and tougher seals. Today, those same traits make them prized by audiophiles for their low noise, long life, and unmatched consistency.
Learn more about JAN / Military-Spec Tubes
New Box vs Original Box
Listings with Original Boxes include the original boxes from the tube manufacturer—in many cases a collector's item.
Listings with New Boxes include plain packaging.
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