I have some voltage questions!!!!

[Robert M. Martinelli]

"new" capacitors?

I have access to a boxful of capacitors I found at the back of the garage, many of which are rated at 450, 500, 600v so should be adequate. Have checked them with resistor and meter to make sure none were holding any charge, none were. I am 99% certain that they were purchased brand new many years ago and have never been used.

Hi,
be aware that having a lot of "new" electrolytic capacitors that have laid on a shelf for years doesn't mean they will work properly, their shelf life is not infinite; in fact we have previously covered this topic in another thread, but be aware that electrolytic capacitors' shelf life is indeed shorter than their operating life, as the loading/unloading process helps keep the electrolyte in good conditions, while the electrolyte is subject to alterations if the capacitor is left on a shelf or inside a box for years. Another thing you can stumble on is that they develop an ESR ( Equivalent Series Resistor ) - something like having a series resistor inside the capacitor that keeps it from working properly, and the bad news is you need specific instruments to spot it, so IMHO you' d better make your life easier and buy a set of new caps, you' ll spare yourself countless hours of frustration and will make also things safer, as there will be no chance they can explode when powered.

Hope this helps

Best regards

Bob

[Spookyman]

Thanks for the advice guys. I do not think that they are electrolytics though. They are orange plasticy looking things, some say Sprague on them which I believe was a manufacturer. From a couple of brief internet searches it sould appear that they are "polypropylene". Would these suffer the same shelf-life issues? or are the odds are that they will be ok?

[tubeswell]

Unless the polyprop/film caps are physically huge, they will not be any good for filter caps because of the relatively large capacitances you need - e.g. starting at 16uF and going upwards.

Check the coding on the film caps you have - I suspect that unless they are physically huge, they won't be large enough capacitances. (I've attached a cap code chart to this post - should open in MS Word)

To get 450-600V filter caps that will conveniently fit into your amp, you will need electrolytics probably - unless you mount the big polyprops in a large box somewhere handy to the amp ;-)

The polyprop caps are good for coupling caps and bass/mid caps in tonestacks.