Audio Research I/50

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.

Yes. All of these factors figure into the total lifespan. Some more than other. At the time, I was playing music 4-5 hours a day (more on weekends) and got about two years from ARC factory tubes. You can probably compare tube bias to the idle speed on a car. If your idle is set to 4000 RPM, your gas won't last as long.