10 watts, or smaller "combo" amps with relatively low wattage (15 to 20 watts) and a single 10" speaker. Mid- to large-size "combo" amps with 30 to 50 watts and one 12" speaker or four 10" speakers are best for high-volume situations, such as band rehearsals and onstage performances. For large venues, such as outdoor music festivals, guitarists may use one or more 100 watts (or several hundred watts) heads with one or more 8x10” cabinets. Vacuum tube Vacuum tubes (called "valves" in British English) were by far the dominant active electronic components in most instrument amplifier applications until the 1970s when solid-state semiconductors (transistors) started taking over. Transistor amplifiers are less expensive to build and maintain, reduce the weight and heat of an amplifier, and tend to be more reliable and more shock-resistant. Tubes are fragile and they must be replaced and maintained periodically. As well, serious problems with the tubes can render an amplifier inoperable until the issue is resolved. While tube-based circuitry is technologically outdated, tube amps remain popular since many guitarists prefer their sound. Tube enthusiasts believe that tube amps produce a "warmer" sound and a more natural "overdrive" sound. Solid-state Most inexpensive and mid-priced guitar amplifiers are based on transistor or semiconductor (solid-state) circuits, which are cheaper to produce and more reliable, and usually much lighter than tube amplifiers. Solid-state amps are less fragile than tube amps. High-end solid-state amplifiers are less common, since many professional guitarists favor vacuum tubes. Some jazz guitarists favor the "cleaner" sound of solid-state amplifiers. Only a few solid-state amps have enduring attraction, such as the Roland Jazz Chorus. Solid-state amplifiers vary in output power, functionality, size, price, and sound quality in a wide range, from practice amplifiers to combos suitable for gigging to professional models intended for session musicians who do studio recording work. Hybrid A hybrid amplifier involves one of two combinations of tube and solid-state amplification. It may have a tube power amp fed by a solid-state pre-amp circuit, as in most of the original MusicMan amplifiers. Alternatively, a tube preamplifier can feed a solid-state output stage, as in models from Kustom, Hartke, SWR, and Vox. This approach dispenses with the need for an output transformer and easily achieves modern power levels. Modeling Microprocessor technology allows the use of digital onboard effects in guitar amps to create numerous different sounds and tones that simulate the sound of