Power output of tube amps compared to solid states

Sorry, Marakanetz, that explanation is not correct. First off, not all tube amps have output transformers. Mlsstl put his finger on the issue- odd ordered harmonics.

Smooth clipping is less odd-orders. Music is a very transient sort of waveform- when the transients clip the amp (even though the rest of the waveform does not), this will be a major factor in what separates the tubes from the transistors, **not** low frequency bandwidth. Odd-ordered harmonics are used by the ear/brain system as loudness cues; the transistor amp overloading on transients will be sounding very loud, whereas a tube amp might still seem to be asking you for more, without the associated harshness.

This is why guitar players prefer tubes as well.

BTW the difference between 250 watts and 100 watts in only about 4 db- not that much to the human ear.

The why rather than the how:

1) instantaneous power as it relates to distortion. In a very short increment of time, tubes can put out a lot more power than transistors or FETs for a given distortion level. This has mainly to do with electron mobility being a zillion times higher in a vacuum than in doped silicon, not to mention asymmetrical drift velocity issues in silicon. But I'll digress here. This is why 'soft clipping' is possible.

2) overload recovery of tubes is much better than solid-state. This is a follow-on to #1. After a transient, there is no reactive impedance to charge recovery in a vacuum like there is in semiconductors. This prevents frequency domain disruptions in tubes (the messing up of harmonics). This is the main point Lavardin has tried to resolve with their own solid-state devices.

There are other more-minor factors mired in the nitty gritty of device physics but these two are the most important, as I see it.

When it comes to steady-state signals, the power levels ARE the same if the Watts are the same. But music is most definitely NOT a steady-state signal. Nearly all measurements and graphs you will see on the performance of an amplifier are based on steady-state. These cannot be used to accurately explain transient phenomena. They can give an overall indication of performance ability, but nothing more. This is why many people believe measurements do not describe how a component actually sounds.

Getting back to the post, efficiency is a separate issue from power output. For Forests, a 50 or 60W tube amp will be great. We had a 55W Cayin on a pair for a long time and it was wonderful. Their impedance is high so they do not demand lots of current, making tube amps the way to go with Forests IMO.

Arthur

Atmasphere,
my due respect to your OTLs, they are money-no-object electronics for whoever can afford to spend extra $$$ for nearly twice larger amount of tubes per channel for the same desired output power vs. an amp with output transformer.

speaking of power compare in plain English, 100Wpc amp wouldn't 'reach' to 12" woofer... you wouldn't even see it's moving unless you crank the volume levels high; while 250Wpc amp would move the 12" woofer at the same sound pressure levels... so 4db also has diversified meaning towards full range.

Marakanetz, not to be on your case or anything but while we do go for as much performance as possible at the same time we take advantage of the vintage look to keep the overall cost down, making our amps affordable against similarly-powered tube amps.

The idea that larger woofers are harder to control is pure mythology and a common one at that. My speakers at home have dual 15" woofers per side and our little S-30 can put plenty of excursion on them.

The amount of excursion a speaker has can be extremely variable as all speakers have different damping requirements. IOW it is not the case that the higher the damping factor the better- in fact there are no known examples of any speaker needed more than a damping factor of 20:1, yet there are cases of speakers that need damping factors as little as 0.1:1 (usually these are designs intended for open baffle).

If the amplifier under-damps the speaker, you actually get excessive excursion rather than too little, and vice versa if the the speaker is over-damped.

Rrog -

I was talking 'peak' power, not steady state.

http://www.the-planet.org/dynaco/Amplifier/Mark%20III%20review.pdf

see the above for some measured performance.