On Mon, 16 May 2016 17:12:14 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Mon, 16 May 2016 15:47:04 +0100, Eiron
wrote:

On 16/05/2016 14:35, Don Pearce wrote:

This is worth a read. It describes an upgrade that reduces gain by
10dB - designed to match the higher output levels of more modern
source.

http://www.desmith.net/NMdS/Electron..._upgrades.html

Basically it is a change to the feedback circuit around the input op
amp, originally 330k/22k for a gain of 23dB, now 100k/22k which gives
a gain of 13dB. Does that sound about right?


Upgrade? That's a bit of an exaggeration. And it's simply not true that
25 year old electrolytics will need replacing. They might, but if they
measure OK, they are OK.

If I had gone to the trouble of unboxing an old amp, I would certainly
change any 20 year old electrolytics. I mean, you have to unsolder them
from the circuit to measure them so why would you put end-of-life caps
back? Just stick new ones in. If the amp was worth the effort to strip,
it was worth new caps.

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.

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.

d

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus