 With the exception of the Red Tremolo module (which usually fails), 95% of these circuits continue to function after 45–50 years.For those that need repair, the Standel website (www.standelamps.com) post all known epoxy module schematics to help technicians repair these amplifiers.In 1970, Standel unknowingly received a batch of defective output transistors that, over time, failed with a burst of direct current that also destroyed the speakers.