The requinto guitar
Information about requintos on the World Wide Web is rather sparse, and as a result, this page is one of hago.org.uk's most visited.
The requinto guitar (or simply "requinto") exists in several guises, but the most common is the 6-string requinto with a 535mm scale tuned A D G C E A - more on the next page. The requinto teams up with the classical guitar and either the contrabass or guitarron to form the "trio romantico" - a group in which the instruments are tuned in E (classical and contra) and A (requinto and guitarron).
It's always risky to make a generalisation, but South American requintos often have a deep body whereas the Spanish models are often proportioned like a slender guitar, as in the Raimundo 1498, which hago owned in our early days, and which is pictured here.
hago experimented with a requinto early on, but chose to move to alto guitars to gain an extra note and to play in the same key as the bass guitar, so that we play in two keys, not three.