What Made Valve / Tube Amps Desirable To Guitar Players?
Back in the 1950s people designed amplifiers to minimize distortion, whether the end purpose of the amplifier was for hifi, pa or guitar. But designs needed to accommodate a variety of inputs, and guitar pickups put out a lot of power compared to most other sound sources.
So amplifiers for guitar use were designed so that they would be sensitive enough to amplify a low-level input, but had enough “input capacity” to allow them to be driven hard without being damaged. That is called headroom – the input might have a 5mV sensitivity, but it woulkd stand being fed a 800mV signal without giving up the ghost. Plug a guitar into a hifi amp and you are usually in danger of blowing the input stage.
Guitarists liked the slight distortion (or as Charlie Watkins used to say, coloration) that developed when the input stage became a trifle overloaded, and that is what most people mean when they talk about the “valve sound”. If, to use a colloquialism, you “dime” one of those old amplifiers, you also get the characteristic bark of the output stage overloading.
When transistorised amps started to gain popularity, many guitarists didn’t like them. They had clean headroom on the inputs, so the customary distortion was not available. They were lighter in weight and they were popular for PA, but they were too clean for many guitarists. Another problem with early high power solid state amps was that they needed a lot of stages in the design to get high power, and that introduced a perceptible delay between picking a note and the sound coming from the speaker.
Nowadays the transistorised guitar amps have been refined with circuits that emulate the sound of the old valve / tube amps, becase those are the sounds that most guitarists want, and there’s hardly a hint of that old “delay” problem. But people still want those old-fashioned amps, and they pay more to buy them. Why?
Whatever the SS amp designers do, they are still only getting close to the actual feel of playing through a valve amp. I said hardly a hint of that old “delay” problem, but the sensitive among us still notice it. Most valve amplifiers only have two or three amplification stages between the guitar and the loudspeaker, whereas any transistor amp has MORE, and if it has built-in effects that only adds to the delay.
Valve amps can usually be fixed if they break down. They are relatively simple, so a repair can take a lot less time than repairing a SS amp.
A lot of transistorised amps are very complicated, so many devices per chip, and built by robots that can solder components which human hands cannot. In many cases a dead SS amp can be not worth paying to fix.
People will tell you that the glass components in a valve amplifier are fragile. In practical situations, you handle both kinds of amplifier carefully, and they don’t get damaged much.
If someone says that repairmen see more valve amps than SS amps, tell them that is because the valve amps are worth fixing. Valve amps hold their value, well made examples can be shown to last for 50 years, and then you can often sell them for a lot more than you paid for them because they are vintage and collectible.