Audio Research I/50

Check the manual and get to the installation page.

It said you need get assistance from the dealer or technical guy to get tube bias.

So it is definitely not auto bias.

Besides, they said tube 6550we has about 2000hours. 

And I think it is pretty shorter than normal. But I do not know why.

they say about a technician only when changing tubes.
i agree that it strange that they didn’t mentioned anything about the bias adjustment on the manual.
if it’s no auto or user adjustable it is really bad news.

on the other hand i believe that they aren’t so stupid to produce such a thing that most of the people Will be deterred to buy.
it is something to check carefully.

Guys, it’s a consumer, not an enthusiast focused product.  This is a gateway drug that they’re selling to people who don’t know or care (me) and I doubt they give a crap what you think about auto bias.  You’re not the target market.  Not delivering what a narrow consumer base wants doesn’t make them stupid- they didn’t count on your business.  At some point I may care, but I’ll trade up when I do. 
 

@runwell - "And I think it is pretty shorter than normal. But I do not know why."

I believe the higher the bias, the shorter the tube life.

All of my ARC amps had about a two-Year tube life (6550s).

Carver's latest tube amps use a much lower bias and, therefore, have a 5 or 10 year tube-life (depending on model).

@dweller  You said 6550 in your amplifier last about 2 years,it is matter how long time you run the amplifier and how hard the sound make,right?

If some one maintain in low sound level,the lifespan could be much longer.