Tube Watts vs. Solid State Watts - Any credence?

I've heard numerous times that Tube watts are not the same as Solid State watts when it comes to amps running speakers. For example, a 70 watt tube amp provides more power than a 140 watt solid state amp. Is there any credence to this or just sales talk and misguided listeners? If so, how could this be? One reason I ask is a lot of speakers recommend 50 - 300 watts of amplification but many stores have 35 watt tube amps or 50 watts tube amps running them. More power is usually better to run speakers, so why am I always hearing this stuff about a tube watt is greater than a solid state watt?

djfst10-09-2015 3:07am

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kijanki Details Discussions Posts This discussion Message User 3,575 posts 10-09-2015 at 02:50pm Copy Comment URL Report Comment Edit Delete The difference in perceived loudness between 70W and 140W amplifier is only 22%. Tube amps, when overdriven tend to produce "soft clipping" (softer/gradual overdive transition), while SS amp just chops off the peaks producing a lot of unpleasant sounding odd order harmonics. Some SS amp were designed to soft clip, including my class D Rowland 102 (and some NADs) but most of them don't. Overdriving SS amp is not only much more noticeable, but can also damage tweeters because of excessive energy in high frequency harmonics.
mapman Details Discussions Posts This discussion Message User 15,679 posts 10-09-2015 at 05:25pm Copy Comment URL Report Comment Edit Delete Most tube amps soft clip so effects of not enough power are not as unpleasant. Other than that, a watt is a watt. What's different is how far a watt can be made to go. Soft clipping helps. Limited bass extension does as well. These are things that can help make a speaker seem more "efficient". You need exponentially more power to deliver a lower frequency at a certain volume level. That's physics....basically how things work no matter what anyone might claim. That's why a table radio with just a few watts and limited bass extension might sound clean within its limitations at a louder volume.
bombaywalla Details Discussions Posts This discussion Message User 1,957 posts 10-09-2015 at 07:23pm Copy Comment URL Report Comment Edit Delete For example, a 70 watt tube amp provides more power than a 140 watt solid state amp. Is there any credence to this or just sales talk and misguided listeners? it's just sales talk & misguided listeners. No credence to this statement. As Mapman & many others before have written: a watt is a watt tube or solid-state. Ralph Karsten of Atma-sphere has written a paper on power amplifier paradigms: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
bdp24 Details Discussions Posts This discussion Message User 4,908 posts 10-09-2015 at 06:41pm Copy Comment URL Report Comment Edit Delete Kijanki is very right---a hard clipping amp is dangerous to the health of your tweeters. I had a low-powered SS amp burn out a dome tweeter in the blink of an eye when it clipped, and the volume was pretty low.
atmasphere Details Discussions Posts This discussion Message User 7,068 posts 10-09-2015 at 08:50pm Copy Comment URL Report Comment Edit Delete The effect has to do with the distortion of the amplifier. Since a transistor amp clips harshly, its obvious when it happens. A tube amp has a soft clipping characteristic (which can be modified somewhat depending on how feedback is used with the amp). So even though the amp is overloading, as it enters clipping it won't sound like it- and as you push it harder, the higher ordered harmonics become more abundant. Since the human ear uses those harmonics to figure out how loud a sound is, their presence will make the amp sound louder than it really is. This works until the clipping is so severe that the amp starts to break up and makes hard clipping like a transistor amp. If you place a sound pressure level meter in the room, the phenomena will be revealed, which is to say that watts is watts.