Hi, Brian,
thanks for your answer, exactly this is kind of information I need. You know, I'm only musician and to some degree linguist, electronics and repairs are just my biggest hobby - but I think I was successful in all repairs I did in the past despite the lack of theoretical knowledge. But as much as my time allows I want to learn more theory, and try always to find some info on internet, which is sometimes time consuming. So I'm really grateful for advice from professionals like you.
All the best!
Daniel Forro
On 16 Feb, 2013, at 6:50 PM, Brian wrote:
Hi DanielYou only need to change electrolytic and tantalum caps, either when they are old 15 years plus, or when you can see a ring of sediment around the end cap of the positive terminal. This applies to the whole circuit, not just the PSU.Certain makes of paper caps are also vulnerable to aging, this can be seen by a slight crack appearing in the outer case. These should also be changed.Yes always use a higher voltage not lower. With regard to capacitance value, this depends on the specific use in the circuit. If this is a timing device then the value is important and should be matched. To match a specific value use a series parallel combination, but you will need the mathematics for this remembering that for capacitors you use the inverse of the rules you would use for resistors. If you need the maths try Googling. If all else fails I’ll do you a master-class! If the use is in decoupling then higher values can be used OK.So what other components age? Resistors do, especially old one known as carbon composition. The only answer here is to accurately measure the value and if more than 10% different from the stated value then change it for a modern item. Old VOX amps are prone to this, on a recent overhaul I changed something approaching 35 resistors all had changed value by a lot!RegardsBrian G3OYU