Instrument amplifiers come in two forms. First, is the combination, or “combo” amplifiers, containing both an amplifier and a loudspeaker in one unit. Alternatively, the amplifier is separate from the loudspeaker and joined to it by cables. The separate amplifier we call amplifier head and can find it placed on top of one or more loudspeaker enclosures. Such a setup we call “amplifier stack”.

In the case of electric guitars, a stack of one head and one cabinet we commonly know as a half stack. On the other hand, a stack of a head and two cabinets we refer to as a full-stack, double-stack or just stack. Depending on the particular music style we might use a different version. For example, retro heavy metal guitarists would likely use the term stack to refer to a full stack, the presence of two cabinets being implicitly understood. However, jazz guitarists might use the term double stack since two cabinets are an exception in this genre. Heavy metal guitarists might understand two actual stacks when using the term double stack. In such a case, a second amplifier head acts as a slave to the first. Both of them we would find coupled to a four cabinet setup. 

Guitar speaker cabinets may use a variety of speaker size combinations. They can include a 12″ speaker, a 15″ speaker (more common for bass amplifiers than for electric guitar cabinets), two 10″ speakers, four 10″ speakers, four 12″ speakers, or eight 10″ speakers.

Touring metal and rock bands have used large arrays of guitar speaker cabinets just for their impressive appearance. Some of these arrangements include only the fronts of the speaker cabinets mounted on a large frame, but no sound comes out of them at all.

Amplifier stack manufacturers

Marshall is one of the most representative British amp stack manufacturers. The first version of the Marshall amplifier stack consisted of an amp head on top of an 8×12 cabinet. This means one single speaker cabinet containing eight 12″ guitar speakers. After six of these were made, the arrangement was changed to one amp head on two 4×12 cabinets. This made the setup more portable. 

On the American side, the Peavey 6505 half stack is a great option if you’re aiming for a relentless all-tube distortion sound. Rock, hard rock and metal players are common users of this half stack. It incorporates 120-watt power, two channels, and a post-EQ effects loop. Besides that, it’s loaded with 12” Celestion Vintage 30 speakers and high-density plywood construction, which give it a solid tone and excellent durability. 

Another well-known American manufacturer is Vox, which has a rich history developing amplifiers. Compared to other manufacturers from the USA, Vox amps are regarded for their cleaner tones. Known for sounding “chimy”, they tend to produce bell-like presence with a sweet and articulate quality.

U2’s music has the crystal-clear tones from the classic AC30 all over. The Edge used an original ’60s model as the foundation his array of effects would run through. Also, Vox amps often feature built-in reverb and tremolo circuits, allowing you to really embellish your guitar sounds.

One additional manufacturer from the USA worth mentioning is Randall, which focuses mainly on the use of solid-state circuits instead of vacuum tubes. Many of these early FET transistor circuits are still the benchmark for solid-state amps. We can find metal guitarists as a common user of these amplifiers.

https://books.google.rs/books?id=kXyFAwAAQBAJ&dq=Amplifier+stacks&source=gbs_navlinks_s

https://en.wikipedia.org/wiki/Guitar_amplifier