In 1937, Kay began to produce a 3/4 size upright bass, which is widely believed to be their Concert or C-1 bass. Like their guitar manufacturing, the basses were hand crafted by skilled craftsmen using special ordered machinery. They even had a hot stamping machine that could emboss the trademark KAY cursive script. TheEngelhardt-Link company bought the upright bass and cello lines[clarification needed] at the auction of Kay/Valco assets in 1969, and continue to produce the same instrument lines till today. Manufactured in Elk Grove Village, Illinois, Engelhardt basses and cellos are sturdy instruments, widely used by students and touring professionals. The ES9 Swingmaster bass (formerly the Kay S9 Swingmaster), is highly thought-of by jazz, swing, and bluegrass musicians.