845/211 tube amplifiers with kef reference 5?

That will ne be the case with the Reference 5s. You will have peak output of about 100dBs before the amp clips. This is going to mean VERY flabby bass.

Yes as I also said the bass is the problem unless there’s a 4ohm tap, then ultimate loudness is reduced 

Seriously, wouldn’t it make more sense to bi-amp. Get a great 845 for mids and treble and power the bass with a nice, SS amp. Get a used Krell or Chord power amp, even Musical Fidelity to pair with it and the net result will be brilliant.

Yes this would be the best way, put his 845 on Ref 5’s mid/highs terminals, and just a cheap Class-D for the bass, a number of configurations could be done being able to even triamp.

Cheers George

That’s just what sets do, look at ANY SET into the Stereophile simulated speaker load frequency response graph, most sets act like tone controls.

Sheesh! The Stereophile simulated speaker load ignores the fact that SETs do not function a voltage source (Voltage Paradigm) devices. As a result they will 'act like a tone control' (more accurately, will exhibit a tonal anomaly)  on speakers that expect the amp to behave as a voltage source (which is most speakers).

But! If the SET is running on a speaker **designed** for this sort of thing (IOW the speaker is a Power Paradigm device too, which is *all* speakers made before 1955) then there will be no tonal issues and the SET can be neutral other than the coloration brought on by the lower ordered harmonics, which audiophiles call 'warmth' or 'bloom'. Speakers that fall into this category will often have controls on the rear to adjust the speaker to the voltage response of the amp (midrange and tweeter level controls). But some speakers, like Coincident loudspeakers, are simply designed to expect a high output impedance of the amp and don't need the controls.


Put another way George is spreading misinformation, apparently out of a misunderstanding of how tube amplifiers behave.

Yes as I also said the bass is the problem unless there’s a 4ohm tap, then ultimate loudness is reduced

This statement is false. Loudness or sound pressure is a function of power output. If the amplifier is making the same power into 8 ohms as it does into 4 (which is what the taps are for) then the sound pressure will be the same since its power will be the same if properly loaded. Now if the speaker is 4 ohms and you use the 8 ohm tap to drive it, you may find that there is less sound pressure on that tap because the power tube is now loaded at an impedance well below optimal. This will cause it to run hotter since some of the power it makes will be absorbed by the tube itself, and because that is the case there will be less output power available to the speaker (and it will be higher distortion). 

thegreenman OP

Don't listen to Ralph, it won't be a disaster like he's making out, he's got a bee in his bonnet, over something.

They will work up to a point as verdataudio and I outlined.And very good if you just use them for the mids and highs, with a cheap class-D on the bass.Maybe he's got some sort of other agenda with his soon to be released Class-D and got you in his sights.
Cheers George

it won't be a disaster like he's making out, he's got a bee in his bonnet, over something.

'Something' is misinformation. In case there is any question, I am a manufacturer of tube amplifiers that employ zero feedback. I know all too well that such amps don't work on speakers of this type. You're not seeing me recommend our amps here. That should tell you something. I just don't like to see people flush $$$$$ down the loo for nothing.

If the speaker is bi-amplified, then an SET might work on the top. But you'll have to try it with a loaner- you might find that even with bi-amplification (and by that I mean also using an electronic crossover) that the SET still doesn't have enough power even if it can handle the load.

Again, to get the most of an SET, it should not be used past 20-25% of full power.

Dear All,

Thank you so much for your replies. Sorry for the delay as I was heavily bogged down by work. Am grateful to each and every of your replies.

Especially to atmasphere, thanks so much for sharing your views from a tube amplifier designer/manufacturer point of view on SET. I never knew that SETs are not meant to be pushed past their 20-25% mark. Still trying to process and understand some of your more technical comments but am very grateful for your sharing.

Am curious, how about push-pull 845 amplifiers in monoblock configuration? Eg 50w class A, each channel driven by 2 845 or 211 tubes? Would those be sufficient to drive the kef reference 5? 

Thanks