Finding exact firmware for Allwinner A50 devices is challenging because "A50" refers to the System-on-Chip (SoC) used by many different manufacturers, each creating their own specific software builds
www.teclast.com/support. Look for a .img or .pac file.Firmware Download Links
Linux-Sunxi Community: For open-source, mainline Linux support and development, check the linux-sunxi.org wiki, which provides repositories and status updates for A50-based devices. allwinner a50 firmware link
Some specific firmware download links: