Which 300b amplifier for Devore O/96

So I have to redo my list now and make sure I get at least 20-30W in my amps. The options are now limitless with PP tube amps.

New List (as of now): Nagra 300p, Kondo Overture (used only, can't afford new), Shindo Haut-Brion (if I can find one).

@essrand I'd go for a bit more power if I were you. The trick with any amplifier is you don't want to work it hard- its lower distortion and power tubes last longer. BTW as you may have surmised our M-60 works quite well on that speaker.

the bottom line would seem to be that when playing recordings having the kind of dynamic range you described (about 32 db) you are not hearing the Franks at their best.

^^ This.

If you really want to hear what any SET does, to really do them justice, the speaker should be of efficiency such that about 20% of full power is *never* exceeded. With a speaker of only 92dB (and while I'm not a fan of Stereophile, in this regard JA's measurements can usually be trusted), that isn't going to happen unless your listening environment is very restricted.

Put another way, to really take advantage of most 300b SETs, speakers with +100dB is really the only way to do it in an average room in the US.


It is for this reason that out of the list presented initially I chose the Nagra.


But if you want to get more in depth about it, there isn't anything special or magic about the 300b. Its a good tube, but often SET advocates prefer the 2A3. That too is a good tube, but often SET advocates prefer the type 45. So 25 years or so ago, the 300b was the one that had the inside track, by 2003 or so the 2A3 was King, and now its the type 45 and its brethren (sub-1 watt-output).  What's happening here is not so much the tube, but the capabilities of the output transformer combined with that tube. Usually the plate current of the power tube is taken through the primary of the output transformer. The transformer can take a bit of DC, which causes a DC magnetic field (in a push pull transformer, the two aspects of current flow cause a DC cancellation so only an AC field exists). To minimize some of the effects of this (since the DC field leads to saturation of the transformer core), the core has a saw cut in it to vastly reduce the DC aspect. This however makes it less efficient for AC as well. So this leads to two practical aspects: bandwidth and distortion caused by saturation of the core.


In both cases, by simply using a tube that is lower power, this problem is reduced. Practically speaking, the upper limit of power on this account has been traditionally about 7 watts; above that the bandwidth and saturation issues really close in around the designer (not saying they can't be solved, but it gets prodigiously more expensive to turn out a transformer that actually has respectable 'hifi' bandwidth)! That's why the 2A3 sounds better and so on; get away from SET operation and you get away from this problem.


I've run plenty of SETs in my day. They all jive with what I mentioned above- a type 45 amp so far is the best I've heard. But it made so little power (0.75 watts) that for the most part it was impractical. I built a pair of type 45 amps that are push-pull; on the same speakers (which were 100dB; not nearly efficient enough for a 45 SET) they were able to reveal much more clarity in vocals and instrument details- bringing just a greater sense of musicality. The push pull version of the 45 makes about 6-7 watts.


In case it isn't clear at this point, SETs need efficient speakers! When you push them harder, the distortion not only obscures detail but it makes the amp seem 'loud' (hence their 'dynamic' quality so often mentioned). IME, in about 95% of audiophile conversation using the word 'dynamics' you can safely substitute the word 'distortion' without changing the meaning of the conversation, other than to make it more truthful.

By comparison, any push pull tube amp has a greater amount of usable power- instead of 20% or so you get about 90% or so; even though you are playing higher sound pressures, it doen't sound as 'loud'.

To state a fairly obvious point, I would just suggest that you make a point of including recordings having particularly wide dynamic range in your assessment. Such as many recordings of classical symphonic music, if you listen to that type of music. For a given average volume, recordings of music having narrow dynamic range and/or recordings that have been engineered with a lot of dynamic compression are of course less likely to reveal the issues Ralph and JSautter have referred to

:)  OK. These are all on LP.

Wagner Gutterdämmerung, London, Solti conducting, final scene (Immolation scene)Verdi Requiem Soria Series RCA, side 1 track 2 Dies Irae
Black Sabbath 'Paranoid' German white Vertigo press, side 1 track 1.Canto General America Insurrecta Atma-Sphere 3-001
Play any of these anywhere near a satisfying volume and that power problem is easily revealed.

@essrand If I were you I'd be open to more than just the Nagra, but out of your list that would be the one. I personally don't think 20 watts would be enough power though. I see 30 watts as a minimum on my speakers and 60 watts is a lot nicer. I did recently move though and my new listening room is slightly smaller and I've still not sorted out all its differences, but for now its more lively so 30 watts has been enough for now. I think if I can tame the side walls I'll be able to play easier with more power though.


The trick is to really have more power than you're going to need! With SETs, because of how they make distortion, this really means that to hear what they do properly you really shouldn't need to run them past about 20% of full power (otherwise the higher ordered harmonics become more audible). That means to take advantage of many SETs you need speakers that are over 100dB...

@essrand  The O/96 is a great speaker; 2dB less efficient than my Classic Audio Loudspeakers. This is just my experience, but the power of a single 300b is simply insufficient on *my* speakers. Unless you're in a small room or never listen with volumes past 80dB, IMO 7 watts just isn't enough power.

I find about 30 watts is a good minimum, if its clean power. I have a type 45-based amplifier (which is push-pull); it makes the same power as a 300b SET. Its simply not enough power on my speakers for a satisfying volume. Now SETs are different from most amplifiers in the way they make distortion; that distortion interacts with the human ear/brain system to make you think they are louder than they really are. As you turn the volume up, this distortion (higher ordered harmonics) first tends to show up on transients. This is why SETs are often credited with being 'more dynamic than their power would suggest'; a common paraphrase you see in SET reviews.

So if I were you, and you want a 300b-based amplifier, I would go with a push-pull 300b amp. It will be making about 30-35 watts which will really help out a lot. There are plenty to choose from.