Power Trio

Commonly found in rock and roll lineups, a Power Trio is a rock and roll, hard rock, or heavy metal band of three members: one playing electric guitar, one playing electric bass, and one playing drums. They leave out the rhythm guitarist or keyboard player on purpose. The Power Trio is essentially rock and roll with a bare minimum of musicians, with one member, usually bass and never drums, doubling on vocals and the guitarist doubling the rhythm and lead parts. The Power Trio is thus commonly found in bands that stick to Three Chords and the Truth, though the format had its roots in bands that were more experimental with their music.

As an Unbuilt Trope, the trio of singer Elvis Presley, guitarist Scotty Moore and bassist Bill Black laid the groundwork for both the Power Trio and the concept of the rock band.

The Power Trio took off in the 1960s thanks to developments in amplifier technology that allowed for the volume of guitars and bass to increase. From there, the format was popularized in the blues-rock and hard rock genres before spreading to prog rock in the 1970s and falling in popularity in the early 1980s. In this first wave, the format was commonly used by bands that engaged in long, intrinsic improvised solos and bombastic jam sessions. This version of the Power Trio contributed heavily to the development of heavy metal, especially power metal. Some bands at this time took a "3+1" approach, having a core Power Trio with a fourth on vocals. Prog rock also introduced a variation that swapped the guitar for a keyboard, while keeping the same general idea.

After the original wave fell out of favor, the format was later adopted by punk rock and grunge bands in the late 80s and throughout the 90s, finding the stripped-down ensemble to fit perfectly with their stripped down approach to music. Several notable punk bands from this time still exist today. The Power Trio also continued to remain popular in progressive rock, though prog as a whole was in a down period at this time. Today, the Power Trio continues to be used in all varieties of rock.

Wikipedia has a list of notable power trios.

Replace the bassist with an organist and you have an Organ Trio. Remove the bassist altogether and you have a Power Duo.

Not to be confused with what TV Tropes calls a "power trio", which we call, simply enough, a Trio.

Anime and Manga

 * In the "variation that swapped the guitar for a keyboard", the then-unnamed group at the very beginning of K-On! had Mugi on keyboard, Mio on bass, and Ritsu on drums. However, school rules said that a club had to have at least four members, so they had to recruit Yui... and they gave her a guitar, making them no longer a trio.

Comic Books

 * Sex Bob-Omb, The Clash at Demonhead, and Crash and the Boys from the Scott Pilgrim series.
 * Josie and the Pussy Cats

Film

 * Airheads: The Lone Rangers are comprised of Chazz on guitar and lead vocals, Rex on bass guitar and backing vocals, and Pip on drums.

Music

 * The Beastie Boys
 * Blink-182
 * Carcass's original line-up was this before they hired a second guitarist.
 * Cream, the likely Trope Codifier.
 * Emerson, Lake & Palmer
 * The Fratellis
 * Genesis started out as a five-man band but were gradually reduced to this between 1977 and 1998.
 * Grand Funk Railroad, from 1969 to 1971.
 * Green Day (pictured)
 * The Jam
 * The Jimi Hendrix Experience
 * King Crimson for a brief period in the 70s; in the 90s, they billed themselves as a six-man band containing two of these.
 * Low
 * Manic Street Preachers, after the disappearance of fourth member Richey Edwards.
 * Motörhead
 * Averted while Würzel was in the band, from 1984 to 1995 - he shared guitar duties with Phil Campbell, who stayed and is still in the band.
 * Muse
 * Mx Px
 * Nirvana
 * The Police
 * R.E.M. after the departure of drummer Bill Berry in 1997.
 * Rush
 * Switchfoot was this for their first three albums. Their fourth member joined just before they hit it big, and the fifth joined just after.
 * The Tea Party, the recently reunited 90s Canadian alt-rock-with-ethnic-flavour trio.
 * Thin Lizzy, during the Eric Bell era.
 * Van der Graaf Generator, with their most recent works, Trisector and A Grounding In Numbers.
 * Wolfmother's original formation. When the band came back, it was now a four-piece.
 * XTC became one after the band retreated to the studio and drummer Terry Chambers left. They used studio drummers for their albums from that point on until David Gregory finally left, leaving them a duo.
 * ZZ Top
 * A very rare example from Country Music: McBride & the Ride
 * Alkaline Trio
 * Andromeda (UK, late '60s)
 * Ash, Northern Irish rock band. Were a originally a three-peice before being joined by guitarist Charlotte Hatherly, who then left and they are now this again.
 * Atomic Rooster, with their first two albums.
 * Beck, Bogert and Appice; power trio featuring Jeff Beck and former Vanilla Fudge members Tim Bogert and Carmine Appice.
 * Before all the others, there was Elvis Presley, guitarist Scotty Moore, and bassist Bill Black. Drummer D.J. Fontana joined later to make the trio a quartet.
 * Better Than Ezra following the suicide of guitarist Joel Rundell. Jim Payne has yet to be named an official member.
 * Word of God is that it's been offered to him, but he's politely declined.
 * Blue Cheer, with their first two albums.
 * Brazilian band Os Paralamas do Sucesso.
 * Also from Brazil, Legião Urbana became this after the bassist left (the singer took over his instrument on studio).
 * British band Placebo, although they drag around several additional members while on tour.
 * Budgie
 * Egg
 * Hüsker Dü
 * Irish band Altar of Plagues used to have two guitarists, but are now this.
 * J-pop band V6, which did the theme songs for Inuyasha and Eyeshield 21, contains two with the band releasing albums and touring both independently and as a combined group. This is evident in Eyeshield 21, where the Coming Century trio did the first intro song and the 21st Century trio did the second. The two combined to do the Inuyasha theme song.
 * King's X
 * Murdock
 * Pig Destroyer used to be an unusual example: just vocals, guitar and drums, forgoing bass altogether. In more recent years they've had a fourth member in charge of noise and samples.
 * Rage's most iconic lineups have all been rock trios, especially the classic lineup of Peavy Wagner (bass/vocals), Manni Schmidt (guitars), and Chris Efthimiadis (drums).
 * Shonen Knife
 * Sleater-Kinney
 * Soft Machine, from late 1967 to early 1968; featured on their self titled debut.
 * Stoner metal trio Sleep, started out with four members but were most successful after the departure of one guitarist.
 * Stray Cats. The minimalism extended to the drummer who usually only had a bass drum, snare drum, and one crash cymbal.
 * Sunny Day Real Estate were this on their album The Rising Tide.
 * The Melvins up until 2006 - currently they have four members, two of whom are drummers.
 * The Minutemen
 * The Nice, after the departure of guitarist David O'List.
 * The band Pezz, currently known as Billy Talent, started as this before bringing Ian D'Sa in to play guitar so Ben Kowalewicz could stick with vocals.
 * Venom, New Wave of British Heavy Metal band and the progenitors of Black Metal.
 * Whiplash, expect in the 90's.
 * Wolves in the Throne Room's original line-up was this, before they got a bassist in.
 * Wreck of the Hesperus

Organ Trios

 * The post-Roger Waters Pink Floyd is the Organ Trio variant: a guitarist, a keyboardist, and a drummer, and the first two sung. They would hire bassists and extra singers for touring.

Web Comics

 * The newly (as of August 2011) reconstituted Deathmøle (if they even choose to keep that name without Natasha around), in Questionable Content, fits the mold with Marten on guitar, Amir on bass and Hannelore on drums. In the short time since they got back together there's been no mention of adding a fourth member again; granted, so far it's just one semi-impromptu jam session, but clearly Marten has bigger plans this time around.

Western Animation

 * Alvin and The Chipmunks are sometimes a Power Trio or an Organ Trio, depending on the adaptation. When they do, it's Alvin on guitar, Simon on keyboard/piano and Theodore on drums. Canonically, all three are multi-talented with instruments and the most recently films have had Simon on bass, fulfilling the traditional definition.
 * Josie and the Pussy Cats replaces the bass with a tambourine. Like with Alvin, the film swapped the tambourine with a bass guitar, or rather returned to original comics, where Valerie also played bass.
 * The Sonic triplets in Sonic Underground are an Organ Trio, with Sonia on keyboard.
 * The Powerpuff Girls were one in "Mime for a Change", with Blossom on guitar, Buttercup on bass, and Bubbles on drums and lead vocals, with the other girls providing backing vocals.