Solid-state circuits found in guitar amplifiers are often based on a transistor or semiconductor. These amplifiers are in most cases cheaper to produce and more reliable than tube-based versions. They are much lighter and less fragile than them as well.
Solid-state amplifiers vary broadly in output power, size, price, and sound quality. Functionality can go from practice amplifiers and combos suitable for gigs to professional models intended for session musicians that do studio recording work. One of the most iconic is the Roland Jazz Chorus (JC-120), launched in 1975 and very used still to this day. We can say it’s more popular between bassists and keyboard players for producing a cleaner sound without too much distortion. It’s worth mentioning that while some jazz guitarists prefer the solid-state alternative for the cleaner sound, most professional guitarists favor vacuum-tube amplifiers. For that reason, the high-end amplifiers of the former category are less common in the market.
Solid-state amplifiers also contain fewer and less expensive parts than their vacuum-tube counterparts, which require regular maintenance and care. One can easily break the glass-made tubes which also need to be replaced quite often for normal use. Most gigging guitarists might change their power tubes once a year and their preamp tubes every two years. On the other hand, solid-state amps don’t require the replacement of parts. They can continue functioning with all their original components for decades, which is a great money saver.
A disadvantage of the transistor-based amplifiers is the fact that they are not versatile. Tubes produce distortion when they operate. This mellow, sweet distortion we often describe as “warm.” Tube amplifiers on home stereos have that same effect. That warmth is desirable on a lot of instruments, particularly treble-focused ones like an electric guitar. By nature, a tube amp will mitigate some of a guitar’s piercing high frequencies, while adding a desired coloration to all frequencies across the board. Solid-state amps can’t do this. Their pure crystalline sound can be great for some instruments, but it isn’t the right thing for every case.
Another disadvantage they have is that they cannot cope with heavy amp distortion effects. A great example would be Jimmy Page’s guitar tone on the “Stairway to Heaven ” solo. That guitar tone was produced by amplifiers, not pedals or other effects, and it could only be produced by tube amps. A solid-state wouldn’t come close. Therefore, for heavy amp distortion, go tube or bust!