Vacuum-tube (or valve, depending upon which side of the pond you live on) technology spawned the Age of Electronics early in the 20th Century. Until the advent of solid-state electronics near mid-century, hollow-state devices were the only choice. But following the invention of the transistor (after their process fell to reasonable levels), within a couple of decades, the death of vacuum tubes was widely heralded. Yet here we are some five decades later, and hollow-state equipment is enjoying something of a comeback, especially in the music and high-end audio industries. Many issues surround hollow-state audio:

Does it produce—as some claim—better sound? If so, is there science to back up these claims?

How do hollow-state circuits work?

How do you design hollow-state audio circuits?

If hollow-state equipment fails, how do you go about troubleshooting and repairing it?

Can we recreate some of the classic hollow-state audio devices for modern listening rooms and recording studios?

How can we intelligently modify hollow-state amplifiers to our taste? These and other topics are covered in The State of Hollow-State Audio.

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