The modern 5-string Guitarra Baiana  descends from the odd looking Pau Elétrico (="electric log") or Cavaquinho Eletrico, built in the 1940s [1,2] by Adolfo 'Dodô' Nascimento and Osmar Álvares Macêdo in Salvador, Bahia, Brazil. The Pau Elétrico featured the neck or fretboard of a cavaquinho mounted onto a lengthy slab of jacarandá (Brazilian Rosewood), a homemade magnetic pickup and four single strings tuned in 5ths (GDAE, thus like a mandolin), resulting into an electrified cross bewteen two acoustic instruments using an entirely solid body. This combination met the natural requirements of its creators, who had the habit of playing the (single stringed) cavaquinho tuned like a mandolin [3]. Simultaneously, the same approach was used to create a 6-string version of a pau elétrico, with the neck and tuning of a guitar [4]. The instruments are kept by the Macêdo family and remain in playing condition. Dodô and Osmar never bothered to file a patent and allegedly it wasn't until the late 1940s that they became aware of the existance of solid body electric guitars made in the US [5].

The fact that the Guitarra Baiana evolved in an entirely native context is of considerable importance for the history of Brazilian popular music, as it gave the instrument a head start over imported models and styles, which contributed much to its musical individualization. The circumstance that it emerged in the same time frame as important ancestral electric guitars in the US (Les Paul's legendary Log Guitar prototype from 1941 and the patent filed by Leo Fender e Doc Kauffman in 1944) has inspired claims that the solid body electric guitar was invented in Brazil. While such claims appear rather farfetched, it may be argued that the Pau Elétrico can be regarded as the first solid body electric mandolin (considering it's mandolin tuning) as solid body electric mandolins didn't appear in the US until the early 1950's.

Note also that the Pau Elétrico in the image is headless, which adds to its strangely modern look that reminds of a Chapman Stick. This original approach was ahead of its time, predating the headless electric bass and guitar designs of Ned Steinberger  by several decades. Note also that it has a  single sided  headstock (=where all tuners are located on one side of the 'headstock') which is normally thought to have first been introduced with the scrolled headstock designs by Bigsby and Fender around 1947 [6].

NOTES

[1]
Sources vary in regard to the exact year of the pau eletrico's development. According to CAYMMI (2006) Dodô Nascimento had been toying with the ideia of amplifying acoustic guitars since his teens the mid 30s. Reportedly, Dodô and Osmar began developing electrified instruments on a serious basis after seeing a performance Rio de Janeiro based guitarist Benedito Chaves (for details, see 1940s - the Pau Eétrico in the history section) which featured an imported pickup mounted on a hollow body acoustic guitar. According to GÓES (1982), this performance took place in 1941, while according to PAULAFREITAS (2005), it did in 1943. Both authors rely on information collected in personal interviews with Osmar Macêdo. Additionally, a great number of texts and articles mention  1942 — without citing a source — as the year of the Chaves performance.

Considering that it took Dodô and Osmar a good year (PAULAFREITAS, 2005) to come up with solid body prototypes, the first pau elétrico would have been ready somewhere between 1942 and 1944. For GÓES (1982, 2000), Dodô & Osmar were first seen using their solid body pau-elétricos in public in 1944 ('Em 1944, já se apresentavam com seus paus elétricos...'.). According to Osmars' son Armandinho MACÊDO (2002b), this began happening in 1945 ('a partir de 1945 eles já tinham os instrumentos maciços elétricos ....').

In sum, the above data (which are all based on material published after 1982) suggest a birth date of the Pau Elétrico not prior to 1942 and not after 1945.


[2]
In one of the few available sources that are elder than 1972, the Bahian composer Carlos COQUEIJO (1970) writes that Osmar and Dodô began to work on the reduction of feedback in 1946, and that this work yielded results in 1948.

"1946: Dodô began to perfectionate electric guitar pickups. At the time, guitars were using an adaptation [they had pickups mounted onto them] and their [hollow] resonance body was causing feedback effects. Dodô discovered by extensive research that a solid body guitar would not exhibit this problem. After this technological advance, Dodô founded a guitar and cavaquinho duo called the "Dupla Elétrica" together with Osmar.
Carlos COQUEIJO (1970) - Historinha da MPB
Sleeve note on Armandinho Macedos first record from 1970  - Our translation.

Portuguese original:
" 1946:  .. Dodô começou a aperfeiçoar os microfones para violão elétrico. Na época, os violões recebiam adaptação e, como tinham caixa harmônica, davam microfonia. Dodô, após exaustivas experiências, descobriu que um violão maciço, sem caixa, não apresentava este defeito. 1948: Conseguida esta vitória de ordem técnica, Dodô organizou, com Osmar, um novo conjunto, formado de dois instrumentos elétricos - violão e cavaquinho -, que tomou o nome de "Dupla Elétrica"
COQUEIJO (1970)
 
[3]
"...my dad used to play a cavaquinho tuned like a bandolim"
Armandinho MACÊDO (2002a) - Interview with Bruce GILMAN for Brazzil Magazine, Feb 2002
(translation by GILMAN)

The single strings made the instrument easy to pick up for guitar oriented players and faciliated the introduction of typical guitarish sounds  — such as string bending, vibrato, and long legato notes — into it's stylistic and tonal repertoire in the 1970s.

[4]
In the duo and trio formations the instruments were used in, the guitar had the function of supplying the bass lines.  Dodô Nascimento would therefore tune his selfmade electric guitar a whole step down (DGCFAD). (GÓES, 1982)

In the early 1950s, Osmar and Dodô also created an electrified version of a tenor guitar (known as "triolim" or "violão tenor" in Brazil ) a medium sized guitar with four single strings tuned like a tenor banjo (CGDA), which completed their trio formation and resulted in the band name "Trio Elétrico".


[5]
According to Armandinho Macêdo, Osmar Macêdo and Dodô Nascimento first noticed solid body electric instruments made by others when Osmar's brother brought a Hawaiian steel guitar back from a trip to the US in the late 1940s.
"it wasn't until the late forties when my uncle returned from a trip to the United States with a Hawaiian steel guitar that my father and Dodô realized that people in other parts of the world were doing the same kind of research.."

Armandinho MACÊDO (2002a) - Interview with Bruce GILMAN for Brazzil Magazine, Feb 2002 
(translation by GILMAN)

[6]
The exact construction date of the model shown in the image is unclear. Rare original photographs from the  early 1950s of pau elétricos used in trio eletrico performances (see here) show models with solid guitar shaped bodies and "Spanish" (double sided) headstocks.