Microphones in the early days of radio were complicated, messy and performed poorly. Some tried to circumvent this entirely and broadcast the instrument directly over the air, skipping over that whole complicated acoustic "problem." This was the onus behind some of the first forays into electronic instruments. There was some success in this arena: the pianorad, the tromborad, the radio-violin, and even pipe organs modified in a similar manner.I found very little information on the Tromborad. It was invented in 1927. Mr. G.B. Ashton wrote an article on that in April of that year for Radio News. The IEEE referenced it in an overview of such creations in 1936.
The "Radio Violin" was a normal violin with a kind of acoustic pickup. In 1931 Rickenbacher made a guitar with a modern style electric pickup. But it wasn't the first. As early as 1920 Gibson was making electric prototypes, these all used acoustic pickups that were really adapted microphones. In 1926 Fred Roehm and Frank Adsit, designed the "radiano" a contact microphone meant for piano that somewhat bridged that gap. Jazz violinist Stuff Smith would employ one with a piezoelectric pick up as early as 1933. More here and here.
The Pianorad was designed by Hugo Gernsback and built by Clyde J. Finch in 1923. The first version was called a Staccatone. It used twenty-five LC Oscillators, one for every key on the two octave keyboard. The Pianorad was first demonstrated on the 12th of June 1926 on 800 WRNY-AM at the Roosevelt Hotel in New York City. Ralph Christman was the pianist. Ralph was a New York area pianist who also played on WABC. Gernsback's Pianorad regulated the pitch of the squeal emitted by a vacuum tube, the key opened and closed the circuit. Inexplicably, Gernsback gave credit for his Pianorad to Lee DeForest. More here and here.
Ultimately, the Pianorad had a very incestuous story. Gernsback was the publisher of the Radio News and owner of WRNY. The writer at the Radio news that wrote up the Pianorad was Clyde Finch. The station itself had only first broadcast on June 12, 1925, about a year earlier, with special guest... Lee DeForest.