One month old. I bought a tube amp because of this

Little Bear B4-X Portable Dual-Mono Vacuum Tube Headphone Amplifier; Mini Balanced Audio Headphone Amp B4 Upgrade Version​

B4-X adopts 2 groups of independent power supply(+12V and -12V) for 2 op amps, less mutual effects and can drive 300Ω headphones. ③ The circuit adopts dual op amp parallel output, with higher output power. ④ B4-X has 3.5mm and 2.5mm 2 kinds of output interface, suitable for most of balanced and standard headphones.

Mini size and unique design: built-in tube makes you have a tube amplifier which can be held by one hand, convenient to carry and can enjoy HiFi music everywhere. Full, delicate and soft sound: warmer than transistors, independent op amp and power supply inhance the SNR and degree of separation, less interplay and higher sound quality.

With built-in battery protection circuit: battery lets your listening feast without time limitation. It can't be turned on during charging and will power off automatically after fully charged, and charger LED will turn to green.

High-end making material and craft: using gold-plated socket, original nichicon electrolytic capacitor, original DALE resistors and precision ring resistance.