Do tube pre-amps need bias adjustments?

And now you do, Reedthis. Not in the conventional sense (user adjustable), but just like a ss power amp, there are internally ways to alter the bias=voltage at the tube (or transistor) of concern.

Reedthis, there always is some level of adjustment that the manufacturer can make in the operation of the tubes in a given circuit. All "biasing" does is change the voltage at each tube. If the designer included some potentiometers on the circuit board to allow for this, it would be easy for a technician to optimize the voltage for the tube. It is not something an end user would do, typically. For most preamps, this tuning is done with the choice of resistor values rather than a pot anticipating that a tube of a certain type (with certain electrical properties) will be used. Thus, we don't talk about "biasing" a tube preamp, but it's certainly possible to make an ajustment in the voltage being applied if one is prepared to make some adjustments inside the case.
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Well, I guess I don't know anymore than I did when I first asked the question, then. Oh well.

I was surprised to discover that my BAT VK-31 preamp does have bias adjustments. When I sent it back to the company to be upgraded, I was told that the technician biased it for the NOS tubes I had installed in it.

Ssglx,

Yup, got it yesterday. Sounds terrific!
Thanks, everyone, for the confirmations.

Reedthis, you're correct about tube preamps not having a bias adjustment. However, some tube preamps will benefit by having matched pairs for some of the tubes, just as will some tube amplifiers. This depends on the circuit design.

As to amplifiers, most new tube amps today have incorporated an auto-biasing circuit to eliminate the need for the user to make the periodic adjustment.
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I've had 4 tube preamps since the mid '80s and none has provided for bias adjustment. Dave

I don't think they do. Did you get your AE-3 MkII?

you are correct

I own two tube pre-amps and you're right... no need for bias adjustments.