Aging of capacitors within crossover networks

Coupling capacitors in tube amps are famous for degradation, but this is attributed to the high temperature environment and the high dc voltage they see. Film capacitors in a crossover network will probably last forever.

"You don't think the person building the crossover tests them all? This reflects the old fashoned way of thinking about quality control tests.

The modern approach is that the output of a production process is monitored by testing a sample of what is being produced. The test results are used, not to verify that the tested items are good, but to detect if the production process is correct. If tested samples fail, the production process is fixed. After doing this for a while all the output is good, and does not require testing. Quality of the product depends on the production process, not on testing. A small percentage of the output continues to be tested, but only to detect if something goes wrong with the process.

Honest1...NO. NO. NO. Exactly the opposite of what you said. Process control manufacturing produces product that is dead nuts on nominal, even if it doesn't need to be perfect. The process is tweeked until this happens. The old fashoned way was to 100 percent test the product and accept those which are in spec and junk or rework the others. Not only is this more expensive, but it results in an inferior product.

Go to Google, and research Taguchi. His engineering approach also involves design concepts. For example: if a circuit requires a 1 percent or a selected value resistor, the best approach is to go back to the drawing board and redesign the circuit so that it only needs 2 or 5 percent resistors. The brute force (stupid) approach is to spend a lot of time and money on precision resistors.