Who's using Harbeth with tubes, what speaker model and how many watts per channel?

@pdreher 
Yeah sorry I had someone read part of it to me but most importantly the red line is the frequency response measured in axis, green is 10 degrees above, and blue is 30 degrees to the side (lateral).

I have SHL5+ speakers and used the Rogue Audio Stereo 100 amplifier (100 WPC).  
Amazing dynamic and powerful sound.  Much more powerful than my previous 100WPC cronus magnum II.  
Med/ large room.  
4 ohm tap sounded weak and anemic, 8 ohm tap much better.  
The Stereo 100 is actually more dynamic sounding that the amplifier I replaced it with, a Parasound a21+.  Should have stopped while I was ahead.  

most harbeths are nominally 6 ohms, dropping to just above 4-5 ohms in the bass region

my understanding is that tube amps typically have trouble delivering a lot of current (certainly compared to ss amps which happily double their delivered power into 4 ohms vs their standard 8 ohm load specs), thus the care needed in making a tube amp drive loads that are low impedance in nature... furthermore, low impedance is most common and hardest for the tube amp to deal with when it is in the bass region, where cone/motor motion requires the most energy (this current, given a specified voltage level) to produce the strong bass notes

There's a bit of myth being engaged in the quote above and it has to do with math.


4-5 ohms might mean that you have to use a 4 ohm tap on a tube amp. If 50 watts is needed to make a certain sound pressure at that dip in impedance, it will not matter what kind of amp makes that power, it will be the same sound pressure and the exact same current.


Put another way, the current needed to make a certain amount of power is the same, tube or solid state. So if it is making the power for that sound pressure, it **has** to make the current. Power equals voltage times current.


Tube amplifiers are different from solid state in that they don't double power as impedance is halved, but nevertheless they can behave as a voltage source. To do this they simply cut power in half as the impedance is doubled. This is one of the reasons why tube amplifier power is more expensive than solid state.


There is a product called the ZERO (www.zeroimpedance.com) which will allow any tube amp to deal with the impedance. So this is really about how much power is needed to do the job. IMO one of the better tube amps to pair with this speaker is the RM-200.

seems to me ralph that the issue comes from transient response

yes power equals voltage times current, but when much current is needed in a hurry to deliver the bass punch we want, it seems to me that is when tube amps with good transformers, properly leveraged by the tubes, and with a lot of power supply capacity can do better, all other things being equal

i thought it is the nature of semiconductors/transistors that allow them to react faster and also their ability to pass more current without strain or overheating -- once again, given good power supply capability they are gating...

separate question ralph - you make otl amps, how do you handle low impedance loads and are otl’s fundamentally better than transformer coupled tube amps? i think back to my experience in the 90s with fourier otls... man that was quite memorable, those 32 6as7’s lighting up all at once --- wow!!

I have 40th anniversary p3s I use with a Rouge st100 and Rouge RP 5 and with the exception of the kt120s both pre and main are using nos Mullard and tectronix tubes. The mullards adds warmth to the 40th anniversary from which I read can be a bit brighter then the regular p3s. Though I don't have direct experience or have listened the regular p3s so I don't know.