Carver Crimson 275 tube amp

Thanks for the reference, shown below.  I don't doubt that the Crimson would be a good mate for your JBL speakers!  For me, personally, a tube amp without auto-biasing is non-starter.  Tiny screwdrivers and a power-up amplifier are the not the way I roll anymore.  Cheers. 
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ADJUSTING THE OUTPUT TUBE BIAS ON THE CRIMSON 275

The front panel incorporates a bias meter. Turn the preamp volume control all the way down while performing bias adjustments. Use a small screwdriver and adjust the bias control (located on the rear of the amplifier) for 80 mA after the unit has warmed up for about 20 minutes. The normal range to use is from 60 mA to 120 mA, and changes here will vary the damping factor of the amplifier slightly. More current increases the damping factor, whereas less current provides a softer more tube-like sound. The design center is 100 mA, and that should be your starting point if you want to experiment. Personally, I found that I loved the sound best on my speakers when I had it set for their design center of 80 mA. It will vary from speaker to speaker, and most importantly with your taste.

The meter reads the combined current for all four output tubes, and it is normal for this current to vary slightly with changes in power line voltage.

A question to Jim Clark. It is not clear how the biasing function on the Crimson unit works.   I am guessing that one would not need a voltmeter for biasing, but it doesn't appear as though it has auto-biasing.  

Can you explain the biasing procedure?   Thanks.

The proceeder above is correct. Generally the bias is set close from when the amp was ran during burn in. After the amp warms up for a few minutes adjust as needed. Double check in 20 minutes. Personally I set them on 80 mA.. No meter is needed. The front panel meter read bias.

After this start up, you won't need to adjust bias again for years, unless you just want to experiment. The 350s use a similar circuit. I have ran those over 2 years, almost every day, without need to adjust bias. 

Really about as painless as solid state.

Great to learn that the bias setting in not much vary over time.   How do you actually do the biasing.... does it entail using a small screwdriver to adjust a potentiometer, confirming the correct mA setting on the meter on the front.  If so, where are the potentiometer located?  On the top of the amp or on the back.  Is it done sequentially for each power tube?  That is what I am getting at.  Thanks. 

Thanks for the question. There is a single potentiometer on the back panel. It has a slot for a small standard screwdriver. You adjust it and read the meter on the front panel.. After that, it will repeat the same bias setting each time you use it for years. It could vary with incoming line voltage, but that is normally very minimal. Basically, set it and forget it.  

            The Crimson 275 will be showing at Axpona near Chicago April 12-14 room 1215. This is the largest audio show in North America. See axpona.com.  Bob Carver Corp and Jim Clark Stereo will be doing demos of the Crimson 350s, Crimson 275, Alchemy DDP-2 Preamp-DAC-Streamer, Wolf Audio Server and the Bob Carver ALS Loudspeaker System.

            A new, shorter, prototype speaker from Bob Carver will be shown. During development, the new speaker system has picked up the nick name - Half Stack. Although still a prototype, it will be present and ready to sing for you.

            We will be using the new Alchemy DDP-2 Preamp, DAC, Streamer. This Peter Madnick design is one you should hear. Even for those looking for more expensive products, at least hear the Alchemy DDP-2, and use it as a standard to judge others audio performance by. The DDP-2 isn't flashy or machined from solid aluminum, but the high end audio performance and outstanding value is all there.

It would be a pleasure to meet some of you and introduce you to the factory guys from Bob Carver Corp.. Jordon Gerber will be there. Jordon is a degreed Physicist. Jordon has been working beside Bob Carver for over a decade. Bob Carver holds a Phd in Physics and also a degree in engineering, although Bob never advertised his education (like Dr Bose).

Of course, you can always use our Satisfaction Guaranty and hear these products in your own home, anywhere in the mainland USA., without risk or restocking fees. Hope to meet you at Axpona.  
 Sincerely,
Jim