40-50w tube amp for Aerial 9

There are several tube amps like VAC, Manley or McIntosh that will work well with low impedance speakers. As to Dehaviland I have no experience and suggest you call the manufacture. To see if a tube amp would work with the Aerial 9 speaker you would need to know the impedance of the speaker over the entire frequency range. Tube amps work best with high impedance speakers or speakers that have a fairly flat impedance. The impedance of a speaker varys over the frequency range and a tube amp with higher output impedance than a solid state amp exagerates the variance making the speaker sound uneven. You can look at an article at Transendent Sound on Amplifier Output Impedance Why Its Important to better understand the dynamics.

I have been using a VAC PA90 with Thiel CS1.5 speakers that go as low as 3 ohms and have a fairly flat frequency response with a sensitivity of 86db. These amps are about 45 watts triode and 90 watts ultralinear. If you check Manleys website their amps are designed for an 5 ohm impedance.

Shredder, I don't think the amps impedance changes. You would need to look at the impedance graph for your specific speaker. Maybe you can contact Aerial for help, they also might make a recommendation. Or you can contact Dehavilland and tell them which speaker you are trying to use.