HEAD 2 use ECC88 on the input and 6N30P output tubes. One of each per channel. They operate in push pull triode mode with output transformers.
HEAD 2 headphone offer 2W at 50ohms and spots balanced inputs and output. It acts a fully operational balanced tube preamplifier just with the turn of the knob to the Line Out position. Output impedance with RCA at 6 ohms and balanced a na at 25 ohms.