Ray Tubes RESERVE KT88

Ray Tubes RESERVE KT88 – Power and Expression in a Single Tube

The KT88: A British Powerhouse

The Ray Tubes RESERVE KT88 is a beam tetrode with an 8-pin octal socket, introduced in 1956 by the General Electric Company in the United Kingdom. With a maximum anode dissipation of 42 W, a transconductance of 12 mA/V, and a maximum anode voltage of 800 V, the KT88 ranks among the most powerful tubes in its class. Its combination of high output and low distortion has made it the preferred choice in high-end stereo amplifiers for decades. The RESERVE KT88 builds on this foundation through Magic Coating and a selection process that fewer than 5% of each production batch survive.

Magic Coating: Monocrystalline Carbon

The outer glass of the RESERVE KT88 carries the Magic Coating: a layer of monocrystalline carbon that accelerates electron transmission, keeps the glass cooler, and blocks external noise. Consequently, the RESERVE KT88 achieves a lower noise floor than standard new production tubes can offer. Furthermore, the coating improves heat dissipation, thereby extending tube life. Above all, the Magic Coating is both a technical and sonic cornerstone of the RESERVE tier — and the primary reason this tube performs as it does.

Selection and Quality Control

Fewer than 5% of each production batch meet the standards of the RESERVE Collection. Every tube is individually tested for gain, transconductance, internal resistance, noise, and microphonics — in both tetrode and triode connection. An audio engineer then personally evaluates each tube under real-world listening conditions before release. Therefore, the RESERVE KT88 offers a consistency that even the finest NOS tubes rarely achieve. For tube rolling in a KT88 amplifier, this means a predictable and lasting upgrade. Each tube ships with a certificate of authenticity and a user handbook containing burn-in guidelines.

Sound Character

The RESERVE KT88 presents a powerful, full-bodied, and expressive sound. Bass is deep and taut, with outstanding control and convincing weight — particularly well suited to large-scale music with strong dynamic contrasts. Vocals and strings benefit from a richly layered midrange with warm tonality and excellent texture. Treble is clear and transparent, with high resolution and no harshness. Moreover, the dynamic range is exceptionally wide, allowing the tube to handle the contrast between quiet and loud passages with complete ease. The soundstage is large and precisely defined, with excellent stereo imaging throughout.

Specifications

• Tube type: KT88
• Socket: 8-pin octal
• Amplification factor: 8
• Transconductance: 12 mA/V
• Internal resistance (tetrode): 12 kΩ
• Internal resistance (triode): 670 Ω
• Max anode voltage: 800 V
• Max screen voltage: 600 V
• Max anode dissipation: 42 W
• Max screen dissipation: 8 W
• Max anode + screen dissipation: 46 W
• Max cathode current: 230 mA
• Max grid voltage: ~200 V
• Heater voltage: 6.3 V
• Heater current: 1.6 A
• Total height: 119 mm
• Coating: monocrystalline carbon (Magic Coating)
• Pins: gold-plated
• Warranty: 12 months against manufacturing defects
• Available as: single tube, matched pair, or set of four

Frequently asked questions

Is the RESERVE KT88 compatible with amplifiers that also accept EL34 or 6550 tubes?

The KT88 shares the same 8-pin octal socket as the EL34 and 6550 but is not directly interchangeable without adjustment. Some amplifiers are specifically designed to accept multiple tube types. Always consult your amplifier's manual or contact us for advice specific to your equipment.

Is bias adjustment required after fitting the RESERVE KT88?

In fixed bias amplifiers, bias adjustment is always recommended after a tube change. In self-bias or autobias circuits, the amplifier adjusts automatically. If in doubt, we are happy to advise.

When is a set of four needed rather than a matched pair?

A matched pair is sufficient for amplifiers using one KT88 per channel. A set of four is required for push-pull output stages using two KT88 tubes per channel — which applies to most stereo amplifiers with KT88 output stages. Ray Tubes matches all tubes on anode current for maximum balance and consistency.