Newby question on watts...

I have aquired an older amp, Audio Research D-100 rated at 100 watts. Weighs 48 lbs. Sold my 1st amp, a Hafler 220DH rated at 115 watts, but only weighed 24lbs. What am I getting for the extra 24lbs? Nothing/something? If both have the same output, what is the gain for all that extra weight.
Transformers , which tube amps have and transistors don't. There is a general correlation between weight and quality/cost. The heavier the better. In tube amps weight is inescapable . In transistors it is desirable because it indicates bigger heat sinks , power supply etc. There are ways around this , Class D etc. but this it is generally true. Also all watts are not created equal , can the amp maintain it's rating into difficult loads? A good trans. amp will double it's output when the impedance is halved. So an amp , like Krell, that will do this is much heavier , more expensive than one that will not. The rating in watts alone is often misleading as it tell us nothing about the actual performance of the amp. Stan
A much more stout power supply that will double it's output as the impedance decreases, ie. into four ohms it will be two hundred per channel while the Hafler would be doing good at 150wpc at four ohms. Also much larger power reserves. The build quality and parts quality is also much higher.
My guess is both a more rigid chassis and an improved / sturdier power supply. While the improvements to chassis construction can be debated, a sturdier power supply will typically be audibly obvious if one knows what to listen for. This becomes more apparent as the speakers are more difficult to drive and / or volume levels ( dynamic and / or sustained ) are increased.

As a general rule, other than really big heatsinks and / or thick faceplates, a heavier amp is typically "better" than a lighter amp of equivalent power rating. Since all of the power that the amp produces comes from the power supply, skimping there will produce both audible and measurable differences everywhere else. Sean
Thanks for responses. The Hafler went to 170 watts @ 4 ohms. I am using 4 ohm speakers. The Audio Research has never listed their power into 4 ohms? I assume from the beef of the unit that it can easily handle these 4 ohm speakers?
I was a Hafler dealer in the days when the 220 was current, it was a good amp but is now dated. Tube amps have the transformers to couple to the speakers so they are not as sensitive to load impedance as transistors are. The bottom line is how it sounds to you. Tubes and transistors do not sound the same and some will like one and some another. You do not mention your speakers , every speaker reacts in a different manner to each amp , they should be considered as a unit because they represent a complex series of interactions , it is hard to speak of the sound of an amp or a speaker without speaking of the other half of the pair. Stan
I was actually more curious in what I was getting out of my 48 lb amp over the 24lb Hafler receiver, because they both put out 100 watts@8 ohms(both of the same vintage). I was just wondering why a unit needed an extra 24 lbs. to put out the same wattage? Speakers are an old pair of ADS L710's I had rebuilt. Tubes don't really enter into equation. Thanks, Gary.