Nature Boy,
I agree with gdnrbob, that Ralph (atmasphere) is probably the most knowledgeable about driving Magnepans with tube amps. I know Maggies are all a relatively stable load of 4 ohms, only dipping slightly below this at certain frequencies. There are no crazy impedance dips like some electrostatics. I also know there are many Maggie owners who drive them with tube amps, although I think most use more than 40 watts.
I own an older pair of 2.7QR Magnepans and have always driven them with high powered solid state amps, my experience being the more power the better they performed. initially I used a 400 watt class A/B amp and currently use 1,200 watt class D monoblcks. The bass and dynamic range of my spkrs improved with the addition of more power.
Another solution you may want to consider is pairing a good tube preamp with a solid state amp. If you take this route, however, it's important you match the preamp's output impedance to the amp's input impedance, the general rule being the amp's input impedance should be at least 10 times the preamp's output impedance for best performance. If you decide to use a class D amp, however, it's also very important you match the sound of the preamp to your personal sound preference since good class D amps are very neutral and your system' sound will be mainly dictated by the sound of your preamp and sources.
Several Audiogon members have mentioned that Magnepan does not recommend using class D amps with their spkers. This makes absolutely no sense to me because I have found them to be ideal for driving my panels. Class D amps are relatively inexpensive, very transparent, small, efficient, run cool and usually have plenty of power. If you don't find a suitable tube amp at an affordable price, you might want to consider finding a tube preamp you like and match it to a good class D amp. This hybrid approach will likely give you a tube sound without so many tubes to maintain and at a reduced cost.
Hope this helped a bit,
Tim
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