Many headphone enthusiasts dig the warm, rich sound of tube amplifiers, but tubes haven’t been terribly popular for portable applications since the transistor came along. The $485 Continental from ALO Audio delivers tube sound in a portable package, using a pencil-thin 6111 tube. That’s an old Raytheon model that’s no longer made, but the company has secured a supply of new-old stock (NOS) tubes that should last them a little while. The Continental’s output stage uses discrete transistors. The internal lithium-ion battery powers the unit for typically 6 to 7 hours. The Continental is shown here with the company’s new $650 Rx Mk3-B, a portable headphone amp that offers the balanced output feature that until now was found only on exotic full-size headphone amps.