Sales at the Tuba Exchange, which is privately held, will reach $2.8 million this year, he said, a 20 percent increase over last year. He would not disclose profits.

After leaving the symphony, Mr. Simonetti, then married with three small children, tried his hand selling pianos. But ''I was just limping along,'' he said.

In 1988, he met a tuba maker from Nuremberg, Germany, at a National Association of Music Merchants Convention in Chicago. ''He was looking for someone to sell his tubas, and I saw a chance to sell something nationally,'' he said. ''Pianos are a very local business.''

From his years as a musician, Mr. Simonetti knew tuba sellers were few and far between. And no one sold tubas exclusively. Today, the Tuba Exchange's competitors, notably the Woodwind and Brasswind of South Bend, Ind., and the Custom Music Company, in Ferndale, Mich., sell an array of instruments.

''Your level of confidence goes up when tubas are all they sell,'' said Donald L. Strand, principal tubist with the Atlanta Opera and the Atlanta Ballet. He has bought two tubas from Mr. Simonetti and also refers his students at Columbus State University in Georgia to him. Mr. Simonetti also refurbishes tubas and redesigns them to fit players' needs in terms of range and tone.

But the price of a tuba can be steep: typically $3,000 to $7,000. ''Imagine your sticker shock if you're a parent of a kid who wants to play the tuba,'' Mr. Strand said.

Customers of the Tuba Exchange range from novices to concert professionals as well as the major United States military bands. But most of Mr. Simonetti's sales are to schools and universities. He markets the instruments to band directors at various conventions and