Ray Tubes Reserve 300B

Ray Tubes RESERVE 300B – The Legendary Output Triode Redefined

The 300B: A Timeless Reference

The Ray Tubes RESERVE 300B is a triode with a four-pin octal base, introduced in 1938 and long established as the most revered output tube in high-fidelity audio. With an anode dissipation of 40 W, a filament voltage of 5 V, and an amplification factor of 3.85, it is the natural choice for single-ended Class A amplifier circuits. Furthermore, its low internal resistance of 0.7 kΩ combined with a transconductance of 5.5 mA/V allows it to drive loudspeakers of varying sensitivity with authority and precision. The RESERVE 300B builds on this legacy through monocrystalline carbon coating and an exceptionally strict selection process.

Magic Coating: Monocrystalline Carbon

The outer glass of the RESERVE 300B is treated with a layer of monocrystalline carbon — Ray Tubes' proprietary Magic Coating. This coating accelerates electron transmission, keeps the glass cooler, and blocks external noise. Consequently, the RESERVE 300B achieves a lower noise floor than any standard new production tube can offer. The coating is difficult to apply and is therefore used exclusively in the RESERVE tier. Above all, it is the technical foundation behind the tube's exceptional sonic character.

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. Moreover, an audio engineer personally evaluates each tube under real-world listening conditions before release. The result is a consistency that even the finest NOS 300B tubes rarely achieve. For tube rolling in a 300B 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 300B delivers a warm, organic presentation throughout the frequency range. Bass is elastic and layered, with natural weight and excellent texture — never heavy or slow. The midrange is where this tube excels: vocals are expressive and lifelike, with compelling presence and refined decay. Treble is smooth and detailed, free of harshness or sibilance. Furthermore, the soundstage is wide and deep, with stable imaging and strong stereo separation — a hallmark of the finest single-ended amplifier circuits. Dynamic nuance is rendered with speed and accuracy, thanks to the tube's low internal resistance.

Specifications

• Tube type: 300B
• Socket: 4-pin (UX4)
• Power output: 6.6 W
• Filament voltage: 5 V
• Filament current: 1.2 A
• Max anode voltage: 480 V
• Anode dissipation: 40 W
• Cathode current (self bias): 100 mA
• Cathode current (fixed bias): 70 mA
• Transconductance: 5.5 mA/V
• Internal resistance: 0.7 kΩ
• Amplification factor: 3.85
• 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 300B compatible with any standard 300B amplifier?

Yes. The RESERVE 300B is electrically compatible with all amplifiers specifying a standard 300B. Due to the bespoke glass design, the tube may be slightly taller than some vintage equivalents — clearance should be checked in enclosed or compact housings.

Is bias adjustment required after fitting new tubes?

In fixed bias amplifiers, bias adjustment is always recommended after a tube change. In self-bias or autobias circuits, the amplifier adjusts automatically. Consult your amplifier's manual or contact us for guidance specific to your equipment.

When is a matched pair needed, and when a set of four?

A matched pair is suited to stereo single-ended amplifiers using one 300B per channel. A set of four is required for push-pull circuits or monoblocks using two 300B tubes per channel. Ray Tubes matches all tubes on anode current for maximum balance and consistency.