Sizemore - The Ampzillas varied a bit. The original was basically an updated Dynaco 400, both having been designed by James Bongiorno. I have the last version, the GAS 500 which was designed by Andrew Hefly. I would put this 30 year old beast up against any modern SS amp with complete confidence. Your Grandson is a keeper... NEVER part with it. And by all means drive it into a 1 Ohm load if possible. It will sing even sweeter. Bongiorno's word for it was "tubistor".