To my ears, Rumbles don't sound like Ampegs.
Ampeg doesn't seem to be one of the early adapters of lightweight gear. Your choices are not going to be broad. So, if you want to stay with the Ampeg sound, I'd look at:
- the SVT-210AV, 200 watt head with 2x10 for 36lbs.
- The Rocket RB-115 combo, 200 watts with 1x15 at 34lbs.
To get the full 200 watts out of the SVT-210AV, you need an additional cab for 4ohms. I think this also applies to the Rocket as well. I'd figure adding another 26lbs or so to those above to get the full wattage.
If you want a Ampeg 500 watt amp, I think the lightest you can get is the PF-500 with a PF115HE cab at 56lbs.