I use my T1 as a headphone amp (cinch in) and not as a USB DAC.
I wanted to swap the tube to check the difference in the sound.
By mistake, I swapped with the T1 still on. To my surprise, the audio in my headphones continued without tube.
I tried the same connected to my Mac on USB: no audio (or at least very low) when no tube was in the socket.
So apparently the tube is not in the audio-path when you use the T1 as a "straight" headphone amp...
A bit disappointing for a "tube" headphone amp, no ???
Anyone else tried this?