Tubes Vs. Transistors?

Question

Specifically what qualitys of a vaccume tube give it the rich sound that solid state audio equipment often cannot duplicate? Its important to note that both transistors and tubes can spec. out the same and still differ.

Answer 1

The "richness" that you refer to has been pinned down to the slight amount of AC hum that modulates the audio being processed by the amplifier.
While clipping in any amplifier can happen, a well designed, and not over driven system is not going to clip anything. Clipping of the audio is due to either bad design, or the amplifier being over driven by the input signal. Construction techniques for transistors are what improved for better sound from a transistor circuit. While some transistors are specifically built to be switches, and audio transistor can be used as a switch. The original intent of the transistor may have been for use as a switch, but that quickly changed. While technical points already given in the other answers about the harmonics generated in clipping of an audio signal are true, no one in their right mind drives an amplifier into clipping. Besides destroying the music, it is also a good way to destroy a speaker due to transients created from the clipping. The root of the answer to your question does lay in the AC component left in the DC as well as the hum induced by the filaments of the tubes. AC bypass caps in the cathode circuit do their part to minimize it, but enough is still there to give that quality of which you ask.

Answer 2

Tube amps require output transformers because what comes out is wrong for driving the coils in the speakers. And of course it is not DC - it is music which is by definition alternating - sine wave mixes. Microwaves use, I believe, a single tube, the klystron that actually produces the microwaves. The rest is solid state. When transistor amplifiers were introduced, they were praised for their crisp clear sound and precise feed back of the recorded material. But people then discovered that the recorded material included stuff they didn't really want to hear - like mouthing instruments and clicks on the stage - and people divided into those that wanted cleaner recordings and those that preferred the "warm" sound of tubes which covered up the perfect errors.

Answer 3

It has to do with the linearity of the amplifier. Tube designs, particularly using tetrodes, can achieve very good linearity. Transistors, generally, have a problem with their I-V curves being linear over a good range. The result of non-linearity is distortion and the creation of harmonics. One interesting aspect of the "switching" behavior of transistors is the growing use of "Class D" amplifiers for audio, in which the signal is represented by a pulse-width modulated high frequency switching waveform instead of trying to make a linear amplifier.

Answer 4

The simple fact that tubes are voltage multipliers rather than current amplifiers is the key difference.
This give more latitude in the way of a response curve that is not available in transistors.

Answer 5

When tubes are overdriven, they tend to produce non-linear soft clipping which gives even-order harmonics. Transistors "clip" hard (in both satruation and cutoff) and tend to produce more odd harmonics.

For whatever reason, most human auditory senses favor even harmonics over odd harmonics. They sound less harsh.

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Answer 6

The main thing is to match the impedance . Tubes are higher impedance than transistors.