Amplifier recommendations for 86 dB Sensitivity Speakers

@mamifero I forgot some things. 

There is a phenomena known as 'thermal compression' in loudspeakers. Its where the voice coil heats up with bursts of power through it. The more it heats up the more compression.

This is why you read about more efficient speakers being more dynamic- with less efficiency (or sensitivity) the bigger this problem is. Vented pole pieces and the like certainly help, but do not solve that problem.

Here is advice I give to anyone who owns a tube amplifier:

If you want the most performance out of your tube amplifier investment, consider a loudspeaker that is 8 Ohms or more and as efficient as you can get (watch out for speakers with dual woofers which might be 4 Ohm in the bass but 8 in the mids and highs, which might simply be rated as 8 Ohms or '8 Ohm compatible'). 

All amplifiers regardless of technology make more distortion into 4 Ohms and speaker cables become far more critical too. Quite literally if you could make the speaker be 8 Ohms or more it would sound smoother and more detailed due to the reduction in distortion from the amp. This is especially true of tube amps. 

There is one tube amplifier that was designed specifically to handle low impedance loads: the Music Reference RM-200. You can read reviews of the original and Mk.2 iterations of the amp by Michael Fremer on the Stereophile website, with test bench measurements by John Atkinson. Both men were very impressed with the amp, Fremer declaring the amp his choice for best "reasonably" priced tube power amp. The RM-200 remained in Stereophile’s Recommended Components List for over ten years! Each channel of this stereo amp creates over 100 watts from a single pair of KT-88 tubes, and does so without running the tubes hard (and therefore shortening tube life).

An option to consider is to add a real good subwoofer to augment your speakers, with an external active crossover to filter out the very low frequencies from reaching your tube amp. Removing just one octave of bass (20-40Hz, or 25-50Hz, 30-60Hz, 35-70Hz, 40-80Hz, 45-90Hz, 50-100Hz) cuts your power amp requirements in half! Remove two octaves (20-80Hz) and that figure rises to 75%!! But that is true ONLY if you remove those frequencies from the signal reaching the amp powering the speakers.

By the way, for anyone wanting a dipole planar-magnetic loudspeaker to use with a tube power amp, consider the Eminent Technology LFT-8b. While it is as low a sensitivity/efficiency design as are the Magnepan speakers (around 84dB), the LFT-8 presents an almost perfectly resistive 8 ohm load to the power amp. And, since it has dual sets of binding posts (one for the planar-magnetic panels, a second for the 8" dynamic woofer in a sealed enclosure, for frequencies up to 170Hz), the speaker can be easily bi-amped, drastically reducing the power requirements of the panels. Those panels themselves present an 11 ohm load to the amp, great for tubes. The ET LFT-8b got a rave review by Steve Guttenberg, who stated in his review that he considered the speaker superior to not only every Magnepan he has heard, but also every electrostatic design. I’m not sure I would go THAT far.

I am in agreement with and will now defer to the AI summary provided above which summarizes things very practically,  I would say.

For absolute best results, you want to throw the kitchen sink at those speakers amp-wise.   Class D will help keep things manageable.

In similar situation with my big Ohm F5 speakers, I chose Bel Canto ref1000m (500w/ch 8 ohm, doubles to 4 ohm) as the "kitchen sink" I threw at them about a dozen or so years back  (search my old posts for more info).

This year I moved to latest Class D technology with 200w/ch Class D Audio GanFET amp.   Beefy enough and better performance overall, in particular with the high end and overall detail and dynamics.

Cheers and good luck!  

Hey OP

as others have suggested, try to go to SS based amps, specifically GAN based amplifiers. they sound very analog, similar to tubes. also suggest you use a tube-based preamp to power up the Gan based power amps

my recommendations that you look into are

1) AGD

2) Laiv mono

3) Orchard Audio

4) ClassD Audio amp

the last one is the name of the company

this link:  2 Channel Stereo GaN Amps Archives - Class D Audio 

they seem to have good reviews for a more inexpensive Price

see if they have a 1-month trial

i suggest you put your gear together using your existing amp and see if there is something missing or will you have a "wow" moment. then decide from there

Thank you all for the information, it's very helpful.

Indeed, these Technicns speakers seemed promising, but they might be too demanding for a 75 Watt per channel tube amplifier. Down the road, I will get a solid state or one of those nice Technics integrated (which are not class D, they have their own thing -pretty neat). But for now, I'll look into 89-90 dB efficiency range.

My current speakers are 4 ohm, 90 dB efficient and this Cayin Tube amplifier drives them pretty well, however, I can notice how the sound profile changes when connected to the 4 or 8 ohm tabs, one is a little softer, detailed and linear, while the other tab gives you more dynamics and a V curve sound.