Why Tubes?
The Sound of Tubes
WHY TUBESThe real reason to use vacuum tubes is the quality of sound they produce. Tubes are unique and it’s impossible to make solid state sound like them. If it was possible, we’d be out of business.
The perennial debate over whether solid state sounds better than vacuum tubes will never be resolved, as it’s mostly personal opinion. Solid state proponents point to hot tubes and the need to replace them as talking points. However, no one can argue against the beauty of sound reproduction from a tube.
The hard, brittle, edgy presentation of many solid state components is a sharp contrast to the rich, lush liquidity and 3D sound presentation of a tube component. Tube midrange and treble are smooth, silky, and have crystal clear sound definition. We admit that solid state can usually produce a harder, tighter bass than other tube designs, but because of our Odyssey Circuit, Black Ice Fusion amplifiers have the ability to match and surpass solid state bass.
Legendary producer Alan Parsons (Beatles, Pink Floyd) put it best: “There’s a place for modelling. It’s usually because of budget or convenience. But I’ve always maintained that guitars invariably sound better with a couple of those glass tubes behind them.”
The Glass Envelope
The glass envelope is what contains the vacuum (no air) and all of the parts of the tube, so electrons can flow.
The Filament
The first component that truly is common to all tube types is the filament. The filament is the part of a vacuum tube that you see glowing when the amplifier is powered on. When an electrical current flows through the filament, it creates both heat and light. The purpose of the filament is actually to create heat, and therefore light. It’s not just something to make it look cool. The heat is essential for working with the cathode.
The Cathode
The cathode is located next to the filament so they can best work together. It is negatively charged and has a coating that releases electrons when heated by the filament. That is the whole point of the cathode: to release free electrons into the vacuum tube after being heated. If there wasn’t a vacuum (no air), this wouldn’t work. Electrons work like a magnet, where positive and negative charges attract. After being released from the cathode, the electrons flow to the next component, the anode, due to this charged attraction.
OK, Tubes Sound Better. But What Are They?
THE BASICSA vacuum tube essentially controls the flow of current and amplifies a signal in audio applications. It has the added benefit of providing a touch of that tube distortion, which makes a tube tone more pleasing to the ears. It’s for this reason people still use tube amplifiers and components.
The Parts of a Vacuum Tube: What’s the Sequence?
The filament is the heat generator. Without heat, a vacuum tube will not work. The heat causes the cathode to release electrons towards the anode due to the negative to positive flow of electrons. In the middle is the component signal and grid, where the amplification takes place when there’s a positive charge. This “boosts” the signal (electrons) on the way to the anode, and it exits the tube on the way to the amplifier and then the speaker.
The Types of Tubes in Audio Gear
TYPES OF TUBESRectifier: Diodes
The purpose of a diode, or rectifier, is to turn alternating current from your house supply into direct current, like from a battery. A diode is a two-element tube that does not have the grid mentioned above. Nearly all electronics need to turn AC into DC. A diode tube also needs the help of some capacitors to make this possible.
The rectifier will usually work in conjunction with the transformer. They aren’t always essential in amps. Sometimes the rectification takes place using non-tube-based technology or the transformer alone. We don’t use these, because tube rectification slows the electron response down and causes smearing in the sound.
Examples of diodes: 6X4, 5AR4 / GZ34, 5U4, EZ81
Preamp: Triode Tubes (Small)
A preamp will amplify the signal and prepare it for further amplification by the power tubes, or it will act as 100% of the amplification in small tube audio devices. A triode is the tube that usually does this, and it’s the most common sort of tube. It’s a three-element tube that can amplify the signal. Triodes can combine signals and split them into two separate signals. They can also invert the polarity or phase of a signal.
Examples of triode tubes: ECC81 / 12AT7, ECC82 / 12AU7, ECC83 / 12AX7, 6922 / 6DJ8
Power Tubes: Tetrodes and Pentodes (Large)
Power tubes further amplify and drive your signal. They are required on larger amps in order to drive large speakers. Tetrodes and pentodes are usually used in the power amp section, as they can amplify your input signal much higher than a standard triode. Tetrodes are four-element tubes and pentodes are five-element tubes. They work in a similar way to triodes but have additional elements called screens, usually between the cathode and anode. The screen “screens” the anode and grid, improving performance.
Examples of tetrodes and pentodes: EL84 / 6BQ5, KT66, KT88, KT120 / KT150 / KT170, 6V6, EL34 / 6CA7
Ultralinear and Triode Mode Switches: Why Don’t We Have One?
At low volume and low wattage, the Black Ice Audio Fusion is Class A and only uses the triode side of the power tube. When the volume is increased, and the power requested is more than the triode can provide alone, the amplifier becomes a Class AB push-pull that uses both the pentode side and triode side of the tube.
Some designs offer a switch that turns off the pentode side of the circuit, so it stays in the triode side when the volume is turned up. There are debates on which type of circuit sounds better, and of course no one is wrong. We didn’t hear a benefit while designing and testing the Fusion amplifiers. It was an artificial limit that could introduce unwanted artifacts in some instances. On the technical side, a switch controlling high voltage is just another part that can cause noise and eventually fail.
Although it would make for great marketing, we chose not to include a triode/UL switch for those reasons. It’s preference at the end of the day, and no opinion is wrong. This applies to the Fusion F11, F22, and F35. The FX10h uses only the triode side of the EL84 and is single-ended Class A only.
What Is Tube Rolling?
TUBE ROLLINGThere are different types of tubes from different brands in both the preamp (triode) and power tube (tetrode/pentode) families explained above, and they can all sound vastly different. Some sound better or worse at different points along the sound spectrum (treble, mids, bass), which results in a different sound signature. Every brand’s version of a tube can sound different than a competitor’s equivalent part. Combining tubes from different brands to control the final mix of sound qualities in your amplifier is called tube rolling.
With tube rolling, you try out different tubes in the same slot. For example, you’d compare a JJ ECC83 and a Sovtek ECC83 and decide which you like best. This means you could end up with a range of brands in your amp. With experience, you’ll get to know the brands. So if you think “I wish my tube had more gain,” you could remove 1 of the 4 ECC83s you may have in there and replace it with a Shuguang ECC83.
Note: when rolling power tubes, it’s best to replace a whole set at a time, not just an individual tube.
Do Different Brands of Tubes Have a Distinct Sound?
American Tubes
6CA7: Like the EL34 but with better-detailed highs, open sound, and better bass and dynamics.
6550: Power control tube. Neutral highs, mids, bass, and dynamics.
British Tubes
EL34: Silky smooth highs, focused mids, three-dimensional. Lacks bass and dynamics.
KT77: More musical than the EL34 with better detail. Made to compete with the 6CA7 tube.
KT88: More musical than the 6550 with better detail and higher wattage dissipation.
Russian Tubes
KT120: Designed to sound like an EL34 but with more power.
KT150: Highs and mids of the EL34 with better bass than the 6550, KT88, and KT120. Lasts longer.
KT170: Like the KT150 but with better midrange and transient speeds.
Yugoslavian Tubes
KT90: Electro-Harmonix claims that, despite its different construction, it has similar sound characteristics to the EL34 tube.
Chinese Tubes
KT100: Supposed to be a drop-in replacement for the KT88. Short-lived and generally not well regarded.