Many analog fans make a heartfelt argument that vinyl is only one piece of the puzzle of true audio satisfaction. They claim that for the most enjoyable performance possible, you need to dispense with the transistor and output capacitor altogether and partner your turntable with tube amplification. Let the record state that my own views are nowhere near as absolute as this. I'm listening to a collection of equipment as I type this, some mine and some on review and there isn't a single tube anywhere to be found in it. It is perfectly possible to get amazing performance from vinyl without ever going near tubes. This being said, tube amplification can sound absolutely fabulous, so what are the ins and outs?
Before the advent of the transistor and semi conductor, tube amplifiers were just 'amplifiers' and the only practical way that existed to take the signal from a stylus, radio or tape head and boost it so that it was suitable for a speaker. The principle is simple enough. A tube is a device that uses differently charged sections- the cathode, anode and a control grid to move electrons through a vacuum in such a way as to create an output that can be used to power a speaker. This is the grossest oversimplification of the process going but all tube amplifiers use a scaled version of this principle to work.
In home audio terms, modern tube amplifiers break down into three categories all with their specific pros and cons.
Single ended amplifiers
These are the simplest amps going and the original amplifier design. A single ended amp will make use of a single tube per channel (generally but not exclusively of a triode design) to produce output. Used within their operating envelope, these amps can have commendably low distortion and impressive performance but that operating envelope is rather narrow. Unless you use a whopping tube, power outputs are generally in the single figure range and even with a 'big un' like an 845 or 211 (both of which look like a fifties horror prop), you are unlikely to see more than 25 watts. This in turn means that you need to use a single ended amp with a pair of sensitive speakers to get the most bang for your buck. Done well, the combination can be staggeringly good but doing it well is rarely cheap.
Push pull amplifiers
These amps use a more modern circuit that introduces at least one other tube per channel to allow one tube to handle half the waveform each. This allows for a rather more efficient design and push pull amps can use a larger number of a wider variety of tubes to generate a much higher power output than would be the case for a single ended design. This increase in bang for your buck means that smaller tubes can be used and still give a reasonable power output. Designed with care and using tubes within their designed performance envelope, push pull tube amps can turn in measurements that are not significantly different to solid state designs and power outputs can be impressively high too- albeit with heavy power consumption at the same time.
These are amplifiers that largely run as solid state designs but use tubes either in their preamp section or as a buffer in the output stage. The intention is to give the amplifier some of the qualities of a tube design without the power consumption, weight and general complexity of a 'true' tube amp. As the tubes in a hybrid are generally being used to introduce a 'tube sound' to the performance, hybrid designs can often sound more stereotypically 'tube like' than actual tube amplifiers.
If we accept that a competently designed solid state amp costing no more than a few hundred dollars can produce better measurements than a tube amplifier costing thousands, what are the reasons why people feel so strongly and passionately about them? The answer lies in the concept that not all distortion is equal. When tube amps distort, they tend to do so in what is referred to as Second Harmonic Distortion. This can quite frequently sound appealing to the human ear and this means that tube amps can sound fuller and rather more euphoric than a solid state amp with the same material. Combined with vinyl's own tendencies in this direction, the result can be a sound that is simply more engaging if these are traits you value.
If you fancy some vacuum tubes in your life, there are a few things to bear in mind. Like turntables, tube amps are largely mechanical objects and their performance lives or dies on the quality of components they use. A good tube amplifier needs an excellent power supply and good quality output transformers, neither of which are cheap. If you have a limited budget, you would be best looking at amps that use smaller tubes like the EL84 or hybrid designs from companies like Jolida and Rogue Audio.
Equally important is that like turntables, tube amps have parts that wear out over time and don't generally take kindly to abuse. If you are buying a used tube amp- particularly if it is more than a few years old, you need to check it very carefully for signs of wear and tear. Tube products operate at high voltages and ones in poor condition can be unreliable and in extreme cases, dangerous. Equally, the construction of tube amplifiers is usually such that a competent engineer can bring one back to life if you are prepared to spend a little money doing so.
The other area that is worth mentioning is that for best results with tube amps, it pays to choose speakers that are suitable for use with them. If you only have a few watts at your disposal, you are going to get the best results out of a pair of speakers that are sensitive enough to be able to go usefully loud on a limited input. Companies like Klispsch, Tannoy, Zu and Audio Note all make speakers that can go effortlessly loud on the end of low power amplification. If you have speakers designed for higher power outputs, the results might not be as satisfactory.
If this all sounds a little alarming, one area where tubes can be employed in a cost effective manner is in a phono preamp. They can be extremely effective here as those same distortion and overload characteristics can be very positively employed in these products. Pre-built examples of tube based preamps go from around $250 (although, as with most things in this industry, you can spend many thousands of dollars on one too) and if you are steady of hand and know your way around a soldering iron, you can find all manner of kits for rather less than this.
Ultimately, there is nothing that says you are any less of a music lover because you don't fancy having tubes in your system but equally, the old adage that you should try everything (well, everything legal and sanitary) at least once has some merits here. A well sorted tube system need not cost the earth and can deliver a sound that is uniquely satisfying. If you are planning some changes to your hardware, looking at the tube options in your budget could be the ticket to listening bliss.