Amazon.com: Fosi Audio T20 Bluetooth 5.0 Tube Amplifier Headphone Amp Support aptX HD Stereo Receiver 2 Channel Class D Digital Mini Hi-Fi Power Amp for Home Passive Speakers with 6J4 Vacuum Tubes :
Amazon.com: Monoprice Stereo Hybrid Tube Amplifier 2019 Edition, 25 Watt with Bluetooth, Wired RCA, Optical, Coaxial, and USB Connections, and Subwoofer Out : Electronics
The Miracle of a $150 (or Less) Tube Amplifier - WSJ