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

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.

• #167

Even tubes can improve the sound of Harbeths with SS amps.  While I prefer the H360, H390, H590 with my 30.1's and 40.2's... I did try my Class D Audio (brand) SDS 470C amp yesterday, and found my Harbeths sounded about as impressive as with my Hegel H590. Though, I was using the Schitt Yaggdrasil R2R DAC (which is superb), and the Audio Research Reference 5se tube preamp - which improves the overall sound quality of the 470C. The benefits of this set up is you get the spacious, airy, holographic sound of tubes, but with the bass and mids control of a powerful SS amp.  

So... a class d SS amp, can drive Harbeths very well... if... you have the right class d SS amp driven by the right sources and preamps.

I should also note that I also have just tried my Audio Research Reference 5se tube preamp in combination wth the Audio Research Reference 150se tube amp driving my 30.1’s and 40.2s... and the sound is sublime.

While the bass slam and control is not as great as with the SS amps I noted herein - the details, air and holographic stage is a bit better, and the organic tone, tenor and texture of the sound is a bit better. And the bass may actually may be a bit more real sounding. Real live bass may not have quite as sharp leading and trailing edges as with the SS amps I noted.

Regardless - all of these amps sound superb with the Harbeths - which have impressed me more than I thought they ever could - being box speakers. They sound very much like Quad 57’s, but with more bass slam - which means with the right set up they sound as good as it gets!

M30.1 Here with Air Tight ATM-2 at 80w KT88.
try some Audio research and Primaluna with lower than 80w but prefer more above 60W.
Also prefer KT to EL tubes.