Figure 4 A 50-year-old Z5U capacitor measured just for fun. Its distortion wasn''t as bad as expected. ... The wait 1000 hours is gonna be problematic for most production lines, that''s 41 days. 😉 ... if you use Vishay Vitramon X7R capacitors, they appear to be using classic and well known dielectrics that exhibit what Mark says. Hence you ...