This is the first tube anything I have owned and am keen to try some different valves when funds allow. It has 2 x ECC83 (12AX7) in it as stock, not sure which brand. I've read there is much better out there but have no idea what I am looking for. So is the ECC83/12AX7 like the socket/tube type? What is the ECC83 part and what is the 12AX7 part? Is that the only type of tube that will fit/work in this device? I've read that Genalex Gold Lion are a decent option, is that a decent brand? This stuf