Ray Tubes RESERVE KT88

SELECT is the best KT88 most listeners will ever need. RESERVE is the one you've always wanted: a bespoke, small-batch beam tetrode that Ray Tubes designs from start to finish for hi-fi audio, so you can skip the hunt for matched New Old Stock.

SELECT is the tube you need. RESERVE is the tube you've always wanted.

The Design

RESERVE is where Ray Tubes pulls out every stop. Each tube is designed from start to finish for hi-fi audio and made in small batches, and Ray Tubes says fewer than 5% of production qualifies. The glass bulb is shaped for better heat dissipation and longevity, the metals are high-purity to reduce the chance of flaws, and the vacuum is pulled slowly rather than quickly. A Magic Coating of monocrystalline carbon improves electron flow, helps shed heat, and blocks noise, and the pins are gold-plated. Each tube carries a unique identifier that tracks it through testing.

Every Ray Tubes tube passes a seven-step process in three phases. Phase one checks reliability: soldering inspection under a microscope and a 24-hour burn-in. Phase two measures critical parameters, matches tubes by current draw, and tests for microphonics. Phase three is an amplifier test with listening by Ray Tubes' sound engineers, plus targeted expert listening sessions on randomly chosen tubes.

How It Sounds

Ray Tubes describes the RESERVE KT88 as combining power and resolution: solid, powerful bass with deep, controlled lows; full-bodied, rich mids with excellent texture; clear, transparent treble with high resolution; and outstanding dynamic range inside a large, well-defined soundstage. Positive Feedback's Tom Gibbs heard you-are-there realism, surpassed only by his 300B amplifier, and an effortless sense of scale and authority. Stereophile's Alex Halberstadt described monster dynamics, detail, smoothness, and vivid textures.

Where It Fits

The KT88 is a beam tetrode introduced in 1956 as a variant of the smaller KT66, named for the kinkless tetrode, and it has been popular in high-fidelity stereo systems ever since. Check your amplifier's manual for the tube type, then choose a single tube, a matched pair, or a matched quad for your output stage. Have your amplifier's bias checked whenever you change output tubes. Ray Tubes publishes a compatibility list, and we can check your amp with you.

Warranty and Break-In

Ray Tubes' One Year Warranty covers manufacturing defects for twelve months, tied to the original invoice and the serial number on the box, so it transfers to a new owner. If one tube in a matched pair or quad fails, Ray Tubes replaces the whole set. Give new tubes 48 to 96 hours of use to break in; early quirks such as slight background noise or imbalance usually fade as hours accumulate. Each tube comes with a user handbook with burn-in guidelines and a certificate of authenticity and warranty.

Press Recognition

• Stereophile, Alex Halberstadt, Brilliant Corners (October and December 2025), writing about tube rolling in Air Tight and other amplifiers with Ray Tubes' new-production tubes. Halberstadt wrote that they sounded better than the competition in just about every respect. Read the October column at Stereophile and the December column
• Positive Feedback, Tom Gibbs (August 2025), reviewing the RESERVE KT88. Gibbs called it a next-level listening experience. Read the review at Positive Feedback
• HiFi.nl, Max Delissen (January 2026), reviewing Ray Tubes. Delissen called them the best tubes of their kind he has heard. Read the review at HiFi.nl
• Monthly Audio, Kim Mun-bu (October 2025), calling the RESERVE KT88 a king of expressiveness, not just brute force. Read the review at Monthly Audio

Wondering whether the RESERVE KT88 suits your amplifier, or how many tubes you need? Give us a call. We'll check your amp's tube complement with you.

Specifications

• Tube type: KT88
• Socket: 8-pin
• Max anode dissipation: 42 W
• Max screen dissipation: 8 W
• Max anode plus screen dissipation: 46 W
• Max anode voltage: 800 V
• Max screen voltage: 600 V
• Max cathode current: 230 mA
• Heater: 6.3 V, 1.6 A
• Transconductance: 12 mA/V
• Amplification factor: 8
• Construction: Gold-plated pins; monocrystalline carbon Magic Coating; optimized bulb shape
• Availability: Single, matched pair, or matched quad
• Includes: User handbook with burn-in guidelines; certificate of authenticity and warranty
• Warranty: One year, transferable