As written, output impedance of Nutube is very high (several hundreds k-Ohms) and very far from driving headphone and speaker. This time I just connect "output transformer for vacuum tube" to Nutube as shown in the picture below.

The signal is taken from input to op-amp and the sound is through "pure non-semiconductor". I've confirmed it can drive well for general headphone but I cannot make youtube video by headphone and the output is connected tiny powered speaker.

The actual result can be found in the movie below. The answer is "YES we can make pure vacuum tube headphone amplifier but not power amplifier for speaker driving".