Tested on Jackson 648.  Very well balanced side to side and both tubes.  Both sides on both tubes test right at 100% and hang tough on the life test.  Tested for shorts. They were wrapped and stored in Motorola boxes.  I think the original boxes were damaged and they were carefully repackaged before I got them decades ago. They show no signs of being used.  And they have the much desired black round plates which are thought by many to sound better than other plate structures.  Price is for the pair.