SET 45 Amp Driving Dynamic Speakers

I thought 45s made 2W and one should run them at under 1W draw to keep distortion from growing much.

Is this what you mean by 0.75W?

You can get 2 watts out of them but if you really want to hear what they do its a good idea to run them at a lower voltage (where they will also last longer); in most applications in the old days they were run pretty conservatively. I used to have an old radio that used one and I think it was only good for 0.8 watts or so. But after 70 years in the field it still tested good...

If they really were type 45s, your output power is likely tripled. 45s only make about 0.75 watts or so single-ended. A 2A3 can do 3-5 watts.

A type 45 can make about a 1 watt or slightly less running single ended.

To really appreciate what they can do (which is to say, they usually sound better than a 2A3 or 300b amplifier) you actually do need some efficiency and the only way to get the efficiency you need is with a horn system unless you are in a really small room, perhaps a closet.

If you drive the amp too hard, the odd-ordered harmonics that the ear uses to gauge sound pressure will appear. This causes the amplifier to sound 'dynamic'. In the initial opening post, we can see that this is happening. Its important to understand that this 'dynamic' quality is really the result of distortion appearing on the transients where most of the power requirements exist. Its a physiological interaction with how we perceive sound.

The problem is, once you know this, you can perceive it as distortion, not just 'dynamics' (in about 90% of audiophile conversations, the word 'dynamics' can be safely substituted with the word 'distortion' without changing the meaning of the conversation). So if you have read this far, I may have wrecked it for you.

You can prove this easily enough by obtaining a sound pressure level meter. They are available as apps for smartphones. You will see that its really not playing that loud- it just sounds like it due to distortion.

When I checked my levels in the past, I didn't get much above 90 db on peaks. That was setting it as loud as I would ever want to listen. Most of the time, it was lower than that. 100 db peaks must be painful, not to mention the potential for hearing damage.

If 100 db peaks are painful, either you already have some sort of hearing damage or the amplifier is making a lot of distortion. The measure of any good system is the quality wherein it is not easy to figure out how loud its playing without instruments (sound level meter) or trying to talk to someone beside you and be heard. IOW 100 db peaks should be effortless and relaxed!! Usually when a system sounds like it is loud or verging on painful that is a sure indication that distortion is playing a role.

The usual solution is more power so that the amp will not make distortion.

In Tommy's case, with only about 0.75 watts to 1 watt available, the maximum power before higher ordered harmonics appear is likely about 0.15 watts to 0.20 watts. The sound pressure with the Audio Notes at 1 meter is thus about 90 db (less at greater distances) before harshness sets in. From his comments it appears to me that he is routinely pushing the amp too hard- he is likely further from the speakers than just 1 meter.

Unless he's listening in a very lively environment or in a very small room, the simple fact is that a more efficient speaker will bring out a lot more of the magic that 45s have in spades (I have type 45 amps BTW; my speakers are 98 db and the amps fall flat on their face because they simply don't make the power. My room is 17' x21'.). This is one of those situations where context is everything as Charlesdad points out. For example, as a desktop setup this would be pretty sweet. But for serious home listening I'd want a speaker that was more like 107 db, such as the Hartsfield or something like that.

The magic of SETs comes from the fact that as power is reduced, so is distortion, down to the point where it becomes unmeasurable. When you are running distortion this low, the result is that more detail is revealed as it is not obscured by the distortion due to the human ear's masking rule. A type 45 amp no if ands or buts has wider bandwidth than higher powered SETs- that is why it sounds better. If you really want to hear what that is all about a high efficiency speaker is mandatory.

2nd order can sound good to the ear. Enjoying our system choice is what its about not if its optimal or not, so if you like it dare I say its right.

The concern of course is not the 2nd harmonic, but the presence of the 5th and above.

100 db peaks is definitely desirable in a good hifi system. In fact it should be a basic criteria while choosing the speaker-amp-room combo. But 100 db continuous SPL is very loud.

This. 100 db peaks should be no problem for any system, that is if you want to be able to reproduce 90 db correctly. Most peaks don't show on a sound pressure meter as high as they really are due to their transient nature.

What bothers me is that all the talk about these amps REQUIRING 100 db + efficient speakers dissuades people from even trying a setup like mine.

I think you might be missing my point. Clearly there is something about that type 45 amp you like. My point is that with more efficient speakers you would like it more, as the more efficient speakers can bring out more of that that amp can do right. I am speaking from direct experience here as I have had type 45 amps at home for years.

If using a 45 amp to only reproduce 350 to 2000Hz on a 100 dB/W driver in a 25m2 room and if average listening level is 85-90 dB SPL, would a 45 suffice or be driven to the point where 5th order harmonics become an issue?

Al did an excellent job of answering this.

Since the type 45 can operate with exceptional bandwidth, I would have considered this amplifier to be a good one for the tweeter, where high power is usually less of an issue. Alternatively, if you could operate a mid-range driver with more efficiency, then you would also have a good payoff.

I've often been amused by the comments in Stereophile about how an SET can measure so poorly and yet sound so good- and further that no-one seems to know why. I have to assume that they did not ask any designers when that comment was made.

IMO low distortion is pretty important, and as long as you don't push them hard SETs can have distortion lower than any solid state amp. And when you ask a little more power, you get the 2nd harmonic which is a lot less offensive to the ear (even in large quantities) than the higher ordered harmonics of solid state! So its no surprise why SETs have a following.

My 8watts 300B SET plays on not even horn and not even efficient speakers (marvelous 88dB XTZ Master M2 speakers to hear or have), and yet sounds loud enough. Imagine now with efficient speakers!!!

'Sounds loud enough' is exactly the right term but for the wrong reason! The reason it 'sounds' loud enough is due to distortion. If you were to put the very same amp on a horn system, it would not 'sound' as loud until it was actually playing a lot louder, due to the fact that on a horn system there would be less distortion and so it would not 'sound' as loud.

This is because the ear converts distortion into tonality and in addition, uses higher ordered harmonics to calculate sound pressure. If the system has excessive higher ordered harmonics, it will 'sound' louder than it actually is. A sound pressure meter sorts this sort of thing out really quick! If you have excessive distortion, 90 db might 'sound' pretty loud since the ear's sense of sound pressure will be skewed; if the distortion is absent, 100 db (10x louder) might not sound any louder!