Looks like a new model is out. Sells for the same price as the old. New features include:
A 1.4GHz 64-bit quad-core ARM Cortex-A53 CPU
Dual-band 802.11ac wireless LAN and Bluetooth 4.2
Faster Ethernet (Gigabit Ethernet over USB 2.0)
Power-over-Ethernet support (with separate PoE HAT)
Tube Rolling – The 503HTA supports both 12AU7( ECC82) or 6922/6DJ8 (ECC88) type tubes. Individual Anode Bias Adjustments plus selectable Series/Parallel Heater Drive insure the perfect setup for virtually any tube! See our friends at www.tubedepot.com for some alternate options!
I would try...