In the beginning, tube amps had a maximum power of 30 watts.
Those days musicians mostly got no PA system and the sound of their guitars came from the amplifier directly.
We know from that time, that because of the power of their amplifiers the Beatles were unable to hear their instruments on stage, while the audience in front of the stage heard nothing but their own shrieking and howling.
This was the time when manufacturers started to develop the first 100 watts amps.
Even today there is a great demand for 100 watts amp heads and many guitarists swear on a Marshall Full Stack although the use of such a powerful amplifier is pretty complicated.
In your bedroom you can hardly turn up the volume, in the rehearsal the power of the sound might be a problem too, it is too loud for many small club stages and even at a festival the sound engineer will complain about the amps beam effect which bastardizes the mix.
If you are playing on a big stage you might be ABLE to use a 100 watts amp but because of today’s PA systems you don’t NEED it.
So, why 100 watts?
Many of the legendary amps of the 60s and 70s got 100 watts: the Marshall Plexi and the Marshall JCM800 as well as the Hiwatt Custom 100 and the Fender Twin Reverb.
Their sounds set standards and are unique.
But you have to keep in mind that these amps are only able to sound that marvelous when the power amp is driven to slight saturation and thereby all components are involved in the sound shaping. But at this point their loudness is insane.
Of course, in your bedroom you could turn the volume of a Twin Reverb down to 1 and the sound might be okay but it has nothing to do with the legendary sound of a Twin that is driven to a slight saturation.
There are numerous ways to tame these loud amplifiers: power soaks, isolation boxes, a retrofitted power scaling or beam blockers.
But to be honest, all these attempts are hardly comparable to the sound of a dimed Marshall.
What is the sound I am really looking for?
Mostly, the legendary sounds have been created with small amplifiers.
Although Led Zeppelin used big full stacks on stage, in the studio they frequently used a small Supro Combo (5 watts) for their records.
Similar to the Rolling Stones: everybody is linking the sound of Keith Richards to a Fender High Power Tweed Twin.
But it is widely recognized, that in the studio, he used Tweed Champ (5 watts) and Tweed Harvard (15 watts) amplifiers.
Even Jimi Hendrix, who live exclusively used Marshall Plexis, used Fender amps for recording in the studio.
With these small amps you might be able to get closer to the sound of vinyl records and CDs than by using the live equipment of a band.
15 – 20 watts as a maximum
Speaking for myself, a 15 or 20 watts amplifier is absolutely sufficient.
This amp still has enough power for the rehearsal room and can also be miked easily.
You can spend the saved money for a good in-ear monitor system. By that you can hear your guitar perfectly and the mix lies in your own hands.