Chemi-con Capacitors – Any Good? – Gearspace.com

The printing on the plastic sleeve isn’t what determines a capacitor’s quality. The brand name shouldn’t be your primary consideration. Many different manufacturers produce a wide variety of capacitors. Look at the specs, not the name.
Here’s a prioritized list of what to look for in an electrolytic capacitor:
1. Voltage rating. If it’s lower than the voltage it will see, it will die.
2. Physical size. If it doesn’t fit in the space available, it does you no good.
3. Leas spacing. If you can’t solder it to the board, same problem.
4. Temperature and endurance ratings. Caps are rated to meet spec after a certain number of hours at a certain temp. Run them at lower than the rated temp, and they last longer. High temp caps (105C and up) will last longer than 85C caps.
5. Impedance. Premium caps are generally described as “low impedance” in the data sheets and cattle-logs. You can look at the specs for ESR, , Impedance, and “tan ∂” to compare the performance of otherwise similar caps. The idea is that the best caps are the ones that come closest to an ideal capacitor, which has continuously declining impedance as frequency increases. Of course, even the best capacitors have a point where other factors cause their HF impedance to be higher than ideal.
6. Capacitance. Modern caps are more compact and space-efficient than the older stuff they replace. In many cases, the coupling and decoupling caps in older gear are smaller that would have been preferred, due to space and cost considerations. Recapping is an opportunity to evaluate the circuit and see if more capacitance would offer an advantage. Of course there are instances where increasing the capacitance would be a bad thing. These are relatively rare though: Electrolytics generally have wide tolerances, so they’re not likely to be used in frequency-critical applications.
7. Price. There’s wisdom in appreciating the point of diminishing returns. Not every capacitor NEEDS to be the best possible part. If your power supply is totally hum-free, low impedance, and has plenty of current capacity to handle every signal it will see, then “upgrading” the caps would be a waste of time and money. When it comes to the coupling caps, you’ll find there’s more to be gained by eliminating the need for them rather than trying to find the best possible capacitor. Of course that applies more to design than maintenance.