Tube amps and speaker ohms

Paul , nice post, and in agreement. FWIW, I demoed a KT88 40 watt intergrated (chinese model/low end lab) just to see how well the 88's work out on orch. The amp is the same weight as my JOR, but offer more tubes in the pre section. Very disapointing. The 86 db Thor's sucked the amp dry. So as you say, impedance of 86 db is something not suited for some tube amps. With a impedance that low, would you say that a important factor is how well the transformers are made/output power?
Tyler's Lin Sig Sys though rated 4 ohms, has a higher db rating at 92, so my little JOR was able to actually work the large speaker into good performance, if not excellent performance. I was very surprised as the LSS has 2 more drivers per cabinet to push vs my MTM design. I was surprised the JOR came through, due to the greater sensitivity of the LSS at 92. (in spite its 4 ohms).
Thoughts?

Bartokfan I think you are confusing impedance with sensitivity. Nevertheless, both are factors that influence how well (or not well) your amp will do.

Rule of thumb is to have a speaker with simple cross over design (or better, no cross over), benign impedance curve, high(ish) impedance and high(is) sensitivity.

I will probably get flack from a couple of SET guys for saying this, but I do not believe any single tube is better per se than another at orchestra (or opera, jazz, rock or anything else.). However, not all amps are equal, and some will perform way over what their rated output would suggest they can.

Don’t get bamboozled into buying a huge tube amp to drive tube unfriendly speakers. Get the right speakers and every tube amp will work well (or work as well as it can).

If somebody tells me his speakers worked fine with his 100 wpc plus tube amp but not with his 50wpc tube amp, I run away. That is the speaker I will never want own, even if I get paid to take them. Proper tube friendly speakers will work well with 2 to 3 wpc tube amps.

As far as orchestra/opera goes, I have had good results with all my tube amps on my speakers. These amps were 300B SET (x 2), 6C33 SET, 6550/KT88 SEP, EL34 PP (x 3), 6550 PP, EL84 PP. I’m probably missing one or two, but the point is they all worked great for orchestra because I mated them with the right speakers.

Once you have tube friendly speakers, you can try any tube type and amp configuration and always end with a smile on your face.

Regards
Paul

A 4 ohm speaker rated at 92db? Quite unusual. Lower impedance speakers are almost always much less efficient. Just a thought...

On the topic of loudspeaker impedance and crossover complexity, "simpler" doesn't necessarily translate into "easier to drive". It is quite possible that elements in the circuit that add to the visual complexity are smoothing the impedance curve, reducing the phase angle, and making the speaker a much easier load to drive. Since we don't get to see the crossover and even if we did we probably couldn't reliably predict the impedance curve just by eyeballing it (at least I sure couldn't), the best bet is to look at the impedance curve itself. That is what the amplifier sees, and whether a tube-friendly impedance curve is arrived at by a complex crossover or by an extremely simple one doesn't matter to the amp.

Duke
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