I though that I might post some of my refined and modified Pete Millett “starting student” headphone amplifier designs. Originally, this was a headphone amp that was supposed to cost about $50-75 before buying an enclosure and have very hi-fi sound for easy build and low cost. I have built about 4 of these and one of which is completely unique, even a rarity among hi-fi tube amplifiers as this headphone amp had an active ground stage that still used the tube in the ground position. However in this design, the gain of the ground tube is basically nullified and is used to give proper voltage and maintain perfect impedance and isolation from ground signals. This tube amp has no ground noise and can be used with low impedance/high sensitivity devices. The power supply in the 3-channel was a custom design with LOTS of smoothing capacitance and noise isolation, it even hung up-side down so that transformer hum could be dampened.
Original Millet I made and original schematic: