# Tube Watts vs SS Watts? (was Looking for an amp and the old SS/ tube discussion.)

nroberts wrote:
Angof (removeme) wrote:
....
I'm a little worried about tube amps as a lot of the time it wont be
possible to crank it, and i have been told that tubes tend to be louder,
(particuraly if you have a tube preamp involved). Any thoughts on this or
clarity on this issue appreciated.

Yes, on average a tube amp rated at the same wattage as an SS amp will
be louder...in fact it will usually burry the SS amp.

statement made several times in this NG, but have trouble
accepting this without testing my own assumptions. What
am I missing? How can this be?

Are we saying that the RMS Wattage _output_ for a SS amp
is not as loud as a tube amp? Another way to
measure the power of an amplifier is based upon
"peak" power (watts) ratings. If the manufacturers of
SS amps TEND to list their power levels as PEAK ratings,
then I can see why tube amps rated in RMS watts would
beat them for sound output.

RMS for the uninitiated means Root Mean Squared. This
is effectively .7071 times the peak power rating.
The .7071 is an approx of 1 divided by the square
root of 2.

Using this math, a peak power of 70 watts is approx
50 watts RMS (70 * .7071 => 50).

If however, a SS amp and the tube amp where BOTH measured
to have 50 watts RMS output, THEN barring any differences
in speaker efficiencies, they should both have the
SAME sound power output.

My suspicion is that people often confuse peak power
ratings with RMS ones. Generally speaking, if a power
rating doesn't mention RMS, then you are getting a
peak power rating. To compare with other amps listed
in RMS, use your calculator to multiply it by .7071.

This also leads me to suspect that many SS amps
are often rated in peak power levels. A 50 watts peak
SS amp, is only going to be approx 35 watts RMS.
No wonder that a 50 watt RMS tube amp walks all
over the so-called 50 watt SS amp (which is only 35)!

If this thread comes to a definitive conclusion
(certainly my hope), then I suggest it should also be
put into the FAQ.

Warren.
.

• Follow-Ups:

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