In article , Don Pearce
wrote:
My initial reaction would be to examine them for any physical signs of
distress, and then measure the ripple when the amp was delivering a
reasonable amount of power. That would give me some idea if they'd need
replacing without having to unsolder them. If all seemed well and the
amp passed its specs I'd then decide if they should be replaced or not.
If I were doing this for someone else, I'd also ask them what they
preferred if there was no obvious problem.

Jim

The problem with electrolytics is that they don't just decide to die at
random, they have a definite life curve, and after twenty years, even if
they measure OK, there is not a lot left in them.

Afraid I don't agree with that as something that always applies.

The 'lifespan' of electrolytics will vary depending on how well they were
made, how appropriately the examples were chosen, and how 'hard' their life
has been in terms of applied voltages, currents, temperature, etc.

The electrolytics in some of my amps are now over 30 years old. Each time
I've checked them and the amp performace, so far, they have been fine. Of
course that may end soon. And I'm sure there are examples where the caps
have degraded and need replacing over much shorter periods.

So I can see that it would make life simple and safe for repair work to
presume they should be changed after, say, 20 years. Of course it means
more work and thus cost for the owner, but helps avoid a possible problem a
few years later. Yet it might be that the removed examples would have been
fine if they showed no signs of any real reason to replace them.

Obviously if this was for someone else I would advise them of the
problem that could arise sooner or later, but for me, no, they would all
go.

I was talking a while ago with Mike S. when I he renovated my 626. My
initial wish was to have its thermal delay bypassed, and better bridge
diodes fitted. My reason being that the delays did tend to fail being
electromechanical parts.

However he pointed out that most of the failures were in the first few
years. The ones that survived, in his experience, went on working quite
happily. Given that he has serviced and renovated many more sets than me, I
let him leave the delay in circuit.

One aspect of electrolytics is that they can actually 'self heal'. If used
biassed correctly any leakage current can tend to reform any thinning spots
in the insulation layer. So, used well within their limits, decently made
ones can last a fair time in my experience.

However I *don't* ever repair sets for anyone else. If I did, I'd discuss
such matters with them and let them decide unless I found a clear reason to
replace.

Jim

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