15465550, the Audience 42 is built for transistor amps in an attempt to get more power into the speaker without affecting its apparent sensitivity. But the speaker can be driven successfully with tubes, and while you will need some power, you do not need a power house amplifier- much more than 150 watts and you can damage the speaker.
I would recommend something that has at least 60 watts or so. Some tube amps will drive the speaker very well directly, but IME many tube amps do have troubles with 4 ohms, so my recommendation is to also consider using a set of ZEROs (see http://www.zeroimpedance.com).
If you do this properly, you will find the bass of a good tube amp to be actually better than that of most transistor amps.
I would recommend something that has at least 60 watts or so. Some tube amps will drive the speaker very well directly, but IME many tube amps do have troubles with 4 ohms, so my recommendation is to also consider using a set of ZEROs (see http://www.zeroimpedance.com).
If you do this properly, you will find the bass of a good tube amp to be actually better than that of most transistor amps.