McIntosh Tube Amplifiers:

The McIntosh 275 Tube Amplifier is a startling amplifier. From the moment I turned it on, I understood why it stayed in production for a dozen years, and why mint-condition used MC275s often fetch up to eight times their original purchase price This is a classic. Long after most other amplifiers, tube or solid-state, are forgotten, the MC275 will still be a classic. This is one of the most famous high-end amplifiers ever made. It's also, in my opinion, one of the most beautiful amps ever made.
What's really special about this amp is namely, the quality of dynamic drive. These amps have an amazing amount of forward thrust. They punch out the music in a lively, exciting way - lots of push/pull going on!
A common misconception among amplifier designers is that a single-ended amplifier is high in distortion. The truth is that single-ended triode amplifiers are high in second-harmonic distortion, which is difficult for the human ear to detect even up to 10%. In fact, this may be one of the reasons a single-ended triode amplifier has so much body and life in its presentation. It never ceases to amaze me how some of the golden classical designs of the 1930s were actually more advanced in the sonic presentation of music than some of our more current hi-fi designs. Maybe we really don't have a clue to what hi-fi of today, vs live music, is all about until we listen to some of the more simplistic (in terms of component count) audio circuits from brilliant minds of years ago in comparison to a live musical performance.

The McIntosh 2105 Tube Amplifier When McIntosh created the McIntosh MC2105 tube amplifier to commemorate their 50th Anniversary, even they were surprised by the firestorm of critical acclaim and demand which it engendered. Now they have designed another amplifier for what has become their 2000 Series of Limited Edition Components.
If you've been fortunate enough to spend time with a classic McIntosh MC2105 amp, you know that in addition to having their own distinct look - the famous Blue Eyes power meters - they also have their own distinct sound. Mac amps have their own way of doing things, and the sound they create presents a powerful argument in favor of their approach.

In the most simplistic terms, think of a single-ended triode amplifier as a huge, powerful preamplifier with an output transformer to transform the tube plate impedance to the speaker load. The signal arriving at the front end of a single-ended design is amplified right through to the output in an unaltered state. The more common amplifier designs of today, whether tube or solid-state, utilize push-pull output stages. Without going into deep electronic theory, in the interest of simplicity, the signal within a push-pull design must be altered. The alteration of the waveform in a push-pull design takes place in a stage called the phase inverter. The phase-inverter stage of a push-pull amplifier alters the waveform by splitting the signal into two parts. The signal is split into a +180 and -180 waveform to drive each side of the push-pull output stage in a push-pull amplifier. The advantage of a push-pull design is greater output power and a canceling of even-harmonic products in the output waveform. Of course, this is under ideal conditions. The disadvantages of a conventional push-pull design are third-harmonic and higher-order distortions. The human ear responds to very minute amounts of dissonant odd-order distortions to as little as 1/2 of 1%.
The single-ended triode tube amplifier design, although having less power output, has four critically important advantages. First is linearity and gain stabilization. Second is a substantial reduction of odd-order harmonic distortions. Third is an unaltered waveform within the amplifier (no phase inverter). Without question, the fourth and most advantageous design parameter is the "non-use" of any [negative] feedback (zero feedback). The use of feedback is an age-old dispute among engineers and technicians. To settle the dispute once and for all, one has only to keep in mind that feedback is always after the fact. In other words, the signal has already been amplified once before the feedback circuit detects and corrects it at the earlier stages in the amplifier. If you have heard an audio system in which all the singers seem to have a lisp, with exaggerated "s" sounds and a grainy sound riding along, this is a good old [negative] feedback circuit at its worst.