The Xian Sheng 708B is a real nice sound for low bucks (close to $200 USD). Available in the USA from:
I got mine used from a fellow head-fier and was interested because I have hundreds of tubes, and many of them are type used in this amp. I thought it would be fun to play with in tube changing.
It uses five tubes: 6n1, 6n3, 6Z4 and two 6DJ8/6922. The 6N1 is the front tube in the window, the 6Z4 rectifier is a lone tube in the back, while three tubes in a row are the front 6N3 the middle 6DJ8 left driver, and the rear 6DJ8 right driver. Russian equivalents are 6N1P (instead of the Chinese 6N1) and the 6N3P (instead of the Chinese 6N3).
It sounds OK with the Chinese tubes supplied but improves very much from tube changes.
I first changed the 6N1 for a new Russian military 6N1P EB (from the 70s or 80s). The sound became cleaner and clearer - sounded better with just this one change.
I next changed the Chinese drivers with two Sylvania JAN 6DJ8 and loved the sound with Mike Oldfield's Amorok - beautiful timbre.
However, this CD sounds good with almost anything so later I tried some demanding but well recorded symphonic works.
Started picking up some euphonic coloration in some tones here and there so I switched to some Amperex-Holland. This was a real nice sound and eliminated any euphonic coloration.
However, I wanted to sharpen the soft tone edges slightly so I used one of my favorites - RCA 6DJ8 tubes, stamped UK on the tube, but actually made in Russia. I bought a bunch of these new and they work really well. The Russian 6n23p (EB or IV for military) made before 1985 are as good.
Getting good sound now - you could spend more and not get any better sound.
This is a great choice in a headphone amp at the price point.
The rectifier is a Chinese 6Z4 (not the old non-Chinese 6Z4), but you can't use the 6X4 instead. Don't try.
I next will try some Toshiba 6DJ8, some Mullards (GB made), Russian 6n23p EB, and whatever else I can find. I also will try a Russian miltary 6n3p tube in place of the Chinese 6n3.
The amp nicely drives the AKG K701 and Sony SA5000 BTW.
All the amps I have owned offer good sound. You have to find the one that suits you. Some seem more of a bargain than others, offering sound that matches more expensive ones - at least in my tastes.
The Xian Sheng is an outstanding bargain.
P.S. Toshiba 6DJ8 tubes are good - sharp tone edge and transient attack bite, with good natural timbre. However, this means that if you have an "edgy" CD or source, you will hear the harshness more than with some other tubes (like Amperex-Holland). However the RCA 6DJ8, stamped UK, are the best.
P.S. Works good as preamp in a speaker system. Much above average in comparison with the other headphone amps, that can serve as a preamp, that I have owned. Plenty of gain for my amp (a real problem for other headphone amps as preamps). Well worth the price for use as a home preamp alone.