� 2004 H. Davis
Vacuum tubes were the earliest of electronic devices, and for decades they were the sole basis of the ever-evolving electronics industry. Some of us may remember the early days of television and the TV repairman. In those days TVs broke down frequently. The repairman made house calls just as physicians once did, and he carried a box full of various tubes. The great majority of repairs required no more than the replacement of a tube or two. When TV circuitry went solid state the visiting repairman went out of business - but TVs became better, smaller, lighter, cheaper, and far more reliable.
The invention of the semiconductor transistor in 1947 started as great a technological revolution as that of the triode vacuum tube by Lee de Forest in 1906. As semiconductor science advanced, integrated circuits, the audio op-amp being among the earliest, packed the performance of dozens or even hundreds of discrete transistors into one tiny, efficient, inexpensive, and rugged package. Without solid-state many common and almost indispensable products could not exist - including the computer you are probably reading this on.
Today, high-power radio transmission remains the only area in which solid-state electronic components have not superseded vacuum tubes. In all other applications, tubes are obsolescent or obsolete.
Musicians that swear by their tube amps may disagree. Yes, some tube amps have desired characteristics that may not as yet have been duplicated in solid-state equipment. But there are those that still use huge, heavy, and unreliable tape delay units in preference to small and superior delay pedals, so, to each his own. If you like it use it, but be aware that you may be able to sound just as good or better with far less effort and cost, and with much fewer maintenance hassles and expenses as well.
In guitar amps, where tubes now find their greatest audio application, it is not the tubes alone that account for the "tube sound." The large, heavy output transformer that is unnecessary with solid-state circuitry introduces harmonic distortion, particularly at low frequencies, that can be desirable. Keep in mind though that, like the many pounds of transformer weight, this distortion cannot be eliminated when it is NOT desired.
Practically, there is much more to consider than sound quality alone. Reliability is also important, as who wants their equipment to die onstage, or perhaps worse, start emitting the random squeals and hisses tubes have been known to produce? Transistors and ICs in properly designed circuits last much, much longer than vacuum tubes do. In addition they are far less subject to drift, the changes caused by aging that affect sound quality and require periodic bias voltage adjustment and the expensive replacement of tubes.
Solid-state guitar amps are, for the same output power capability, smaller, much less heavy, lower in cost (particularly ongoing maintenance costs), more reliable, less fragile, and far more efficient. A well-designed solid-state amp can sound like a tube amp, and if not, the use of a good overdrive/distortion pedal like the Pigtronix Disnortion or Polysaturator, or the vintage solid-state Electro-Harmonix Hot Tubes, can make it do so. The advantages of solid-state design are even greater in bass amps than in amps for guitar alone. And the last thing you want under the hot lights onstage in a crowded club in summer is to be surrounded by tube amps that are more efficient as room heaters than as sound producers!
As an engineer as well as a musician, I am not a believer in pedals that contain tubes. Glass-enveloped tubes are relatively fragile and unreliable. Pedals with tubes cannot be powered with an internal battery, as tubes require too much power. A special power supply, large wall-wart, or a line cord is necessary with tube equipment. Tube pedals are significantly larger, heavier, and more expensive than their solid-state equivalents. And tubes are not even necessary to get "tube sound!" Properly designed CMOS or FET circuitry can produce beautifully tube-like even-order harmonic distortion and soft compression, with all the solid-state advantages of low power consumption, no warm-up time, lower cost, and a smaller, lighter, sturdier, more reliable pedal.
Tubes are relatively primitive devices. As they cannot produce an audio delay, they are incapable of generating echo, reverb, chorus, or flanging. Research I have done has shown them incapable of producing decent phasing or vibrato effects as well. Pedals that claim to be tube-based only use the tubes for voltage gain or overdrive distortion. A "tube" envelope-controlled filter or modulation pedal for instance may use tubes for signal gain or buffering, but op-amps, optocouplers, and other solid-state devices generate the actual effects. The tubes are used more as a selling point with tube faddists than as necessary components; in fact they are NOT necessary components.
I once evaluated a prototype "tube" pedal that contained a small light bulb. The bulb had no function other than to light up as tube filaments do; the actual filaments were not visible, so a power-wasting incandescent bulb was included, at the potential buyer's expense, strictly for appearance's sake! In fact it was actually detrimental to the unit's proper functioning due to its light leaking into the optocouplers that did the actual job the tubes were supposedly doing. Whenever I want to laugh, I think of this!
In my professional opinion, tube-based guitar pedals, made mostly by those in the tube manufacturing and sales business seeking to create a market for their wares, are a throwback to an obsolescent technology with no advantages and many disadvantages for this application.
The promotion and use of vacuum tubes in equipment for the audiophile market is even more ludicrous than their use in guitar pedals. It is a RIPOFF, a complete FRAUD upon the consumer! I can prove this assertion in technical detail, but that would be off-topic here.