Hi Daniel
You 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\u2019ll 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!
Regards
Brian G3OYU
From: vintagesynthrepair@yahoogroups.com [mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Daniel Forró
Sent: 16 February 2013 9:00
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Recapping
As I'm in project of recapping my older devices, I'd like to ask all
of you more experienced gurus here your opinion:
1. I started with changing electrolytic capacitors in PSU. Do you
think it would be good to change all electrolytic capacitors in the
machine (on digital and analog boards)? I want to use the opportunity
of opening the machine and to avoid possible problems in near future...
2. Is it necessary to change also all bipolar, tantalum, ceramic,
polyester... capacitors? Do they also deteriorate in time?
3. Is there some age of the device from which would be good to change
capacitors? 15 - 20 - 25 - 30 and more years?
4. When changing old capacitors with nowadays non-existing values, of
course I must follow voltage or use higher value. Concerning capacity
value should I use the nearest higher value, too? Modern capacitors
are usually smaller than old ones, so size is not critical. I'm just
afraid if in certain kind of circuits higher value couldn't be some
problem...
5. Do you have eventually any other tips & tricks for maintenance of
older machines? Of course I do cleaning, reseating IC's in sockets,
cleaning and reseating all connectors, cleaning keyboards... I will
also change displays in about 10 of my machines for modern LED
backlighted types. I disassemble keyboards, clean them, lubricate if
necessary, change key bushings... If necessary, I change
microswitches... And I'd like to upgrade OS EPROM's in some of my
instruments.
6. I have also two old Hammond organ (CV model from 1945 and M3 from
1960). Do you think I should change capacitors (or even more
components) in preamplifier (CV), amplifier (M3), tonewheel generators
and vibrato lines? There are specialized firms offering sets of
capacitors or other components for old Hammond organ.
I will add that all my old machines work well, and I know there's an
old wisdom "don't touch it if it works", but... What's your opinion? I
want to change capacitors because I'm nervous that old machines can
have problems. But is it REALLY necessary to change it when machine
works well?
Thanks for any answer.
Daniel Forro