The classical guitar is quite a quiet instrument and although very widely played in the early years of the twentieth century, it was not used much in bands because it could not compete with the volume of the other instruments. For years guitarists and inventors experimented with different ways of making an electric guitar which could play much louder.
The first electric guitars were produced in the USA before the Second World War by a variety of makers, but the first commercially successful electric guitar with a solid body was made by californian inventer Leo Fender and went on sale in 1950. It was called the Fender Broadcaster. The guitar is still being produced today by the Fender company but it is known, as it has been since 1951, as a Telecaster.
Marching bands are extremely popular in the US and have been since the 19th century. Although bands wanted to use the powerful low sounds of the tuba, it was almost impossible to march whilst playing a large tuba. As a solution to problem JW Pepper produced a different shape of tuba that could be worn around the body. He called it the Sousaphone after John Philip Sousa who composed many famous pieces for marching band.
The Philharmonia Orchestra does not normally use Sousaphones, but it could! Usually composers writing for orchestra write for standard tubas rather than the wrap-around Sousaphone.
Like many inventions the synthesizer was created by the collective effort of many people in different countries adding small improvements and new technologies one piece at a time. The first electric keyboard was a 7 ton machine produced in 1901 and was called the Teleharmonium. It was built as part of the phone system and when musicians played it people all over New York could dial up the instrument and pipe live music into their homes. The improved version two of the machine in 1906 was a 60 foot long, 200 ton monster. Not surprisingly Teleharmoniums didn't really catch on.
The first true synthesizer was built in 1952 by Raymond Scott and was called The Clavivox.
The first really portable, easy to use, programable synthesizer was also produced in the US by Robert Moog. It was called the Minimoog and went on sale in 1970.
Synthesizers are frequently used in orchestral pieces, especially in film music, such as the Lord of the Rings theme music which the Philharmonia Orchestra has performed on a number of occasions.