Guitar Center has a used Ampeg SVT Classic 810 for sale for $599 ($100 price drop). I have no idea as to what year it was made. I plan on going up to see it tonight. Is there any serial number codes I should look for?...or tell-tale signs that it may be one of the "down years" when manufacturing wasn't up to the Ampeg standard? They also have a used 810e they say is USA made for $749. Is one model better than the other?