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How do I find out about the age of these speakers? I have the serial numbers. Is there a link to such a thing on this site?I have been told that they may be as much as 40 years old! They still perform nicely and look great. thanks for any help

We have an old set of heresy speakers they are hwo with seriel number 96u350 and 96u351 both are in excellent cond. and we would like to know just how old they are and their approx. value for insurance purposes. thanks for any help