Fidelity Research FR-64 vs. FR-54

Dear Raul, The below summary comes from the IEEE, not the "AHEE", your fictional bugaboo.  Note the first bullet point under the heading "Transistors-Disadvantages".  I don't want to go back and forth with you any longer.  You are entitled to your listening preferences, whatever they may be, but you are not entitled to create your own set of facts.  

Vacuum tubes – Advantages

• Highly linear without negative feedback, specially some small-signal types
• Clipping is smooth, which is widely considered more musical than transistors
• Tolerant of overloads and voltage spikes
• Characteristics highly independent of temperature, greatly simplifies biasing
• Wider dynamic range than typical transistor circuits, thanks to higher operating voltages
• Device capacitances vary only slightly with signal voltages
• Capacitive coupling can be done with low-value, high-quality film capacitors
• Circuit designs tend to be simpler than semiconductor equivalents
• Operation is usually in Class A or AB, which minimizes crossover distortion
• Output transformer in power amp protects speaker from tube failure
• Maintenance tends to be easier because user can replace tubes

Vacuum tubes – Disadvantages

• Bulky, hence less suitable for portable products
• High operating voltages required
• High power consumption, needs heater supply
• Generate lots of waste heat
• Lower power efficiency than transistors in small-signal circuits
• Low-cost glass tubes are physically fragile
• More prone to microphonics than semiconductors, especially in low-level stages
• Cathode electron-emitting materials are used up in operation, resulting in shorter lifetimes (typically 1-5 years for power tubes)
• High-impedance devices that usually need a matching transformer for low impedance loads, like speakers
• Usually higher cost than equivalent transistors

Transistors – Advantages

• Usually lower cost than tubes, especially in small-signal circuits
• Smaller than equivalent tubes
• Can be combined in one die to make integrated circuit
• Lower power consumption than equivalent tubes, especially in small-signal circuits
• Less waste heat than equivalent tubes
• Can operate on low-voltage supplies, greater safety, lower component costs, smaller clearances
• Matching transformers not required for low-impedance loads
• Usually more physical ruggedness than tubes (depends on chassis construction)

Transistors – Disadvantages

• Tendency toward higher distortion than equivalent tubes
• Complex circuits and considerable negative feedback required for low distortion
• Sharp clipping, in a manner widely considered non-musical, due to considerable negative feedback commonly used
• Device capacitances tend to vary with applied voltages
• Large unit-to-unit variations in key parameters, such as gain and threshold voltage
• Stored-charge effects add signal delay, which complicates high-frequency and feedback amplifier design
• Device parameters vary considerably with temperature, complicating biasing and raising the possibility of thermal runaway
• Cooling is less efficient than with tubes, because lower operating temperature is required for reliability
• Power MOSFETs have high input capacitances that very with voltage
• Class B totem-pole circuits are common, which can result in crossover distortion
• Less tolerant of overloads and voltage spikes than tubes
• Nearly all transistor power amplifiers have directly-coupled outputs and can damage speakers, even with active protection
• Capacitive coupling usually requires high-value electrolytic capacitors, which give inferior performance at audio-frequency extremes
• Greater tendency to pick up radio frequency interference, due to rectification by low-voltage diode junctions or slew-rate effects
• Maintenance more difficult; devices are not easily replaced by user
• Older transistors and ICs often unavailable after 20 years, making replacement difficult or impossible

Dear @thekong : I can't detect it due to that glorious so low distortions in my today system/room.

Dear Lew, ''...you are not entitled to create your own set of

facts''. ''Facts'' is the other expression for true statements.

Our reasoning consist of some implicite or explicite assumptions

(aka ''premisses'') which are believed to be true and deduction from

the premisses. That is why self-deception is the most common kind

of deception.