Balanced Audio Technology VK-56SE power amplifier | Stereophile.com
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 :
English Acoustics Stereo 21c Vacuum Tube Power Amplifier – HCM Audio