[Howard Stone]

Does the sound quality deteriorate as the capacitors deteriorate? Do properly restored amps sound better?

Is an older unserviced amp more likely to go DC?

Does a stitch in time save nine? I mean, are you more likely to save yourself an expensive or even impossible repair if you get it serviced? 

[Trevor Wilson[_3_]]

On 19/02/2019 7:32 am, Howard Stone wrote:
Does the sound quality deteriorate as the capacitors deteriorate? Do properly restored amps sound better?

**Absolutely.


Is an older unserviced amp more likely to go DC?

**Not necessarily. Most employ some kind of protection anyway.


Does a stitch in time save nine? I mean, are you more likely to save yourself an expensive or even impossible repair if you get it serviced? 

**Maybe. Depends on the product, it's age, how it has been used, etc.
Naturally, it is always best to have a product thoroughly checked and
serviced by a TRUSTED person, but with high quality products, not
absolutely necessary. That said, if you follow my previous suggestions
and look at an old Krell, then you would be well advised to have the amp
thoroughly serviced, including electrolytic cap replacement. If, for no
other reason than the fact that the old Krell KSA100 is nudging 35+
years old. If the amp has seen a bit of use, then the main filter caps
(and all the smaller ones) should be replaced, unless it has already
been done recently. A good tech would check the big caps first, since
they can be expensive (but easy) to replace. I've done some old Mark
Levinson amps recently and they use similar main electros. The big
difference is that the replacement in the ML amps is something of a
nightmare. Old Krells are much simpler prospects.I would also consider
re-mounting all the output devices, but that is not essential. In any
case, the old tech's adage applies he 'If it ain't broke, don't fix it.'


--
Trevor Wilson
www.rageaudio.com.au

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

[Peter Wieck[_2_]]

On Monday, February 18, 2019 at 3:32:25 PM UTC-5, Howard Stone wrote:
Does the sound quality deteriorate as the capacitors deteriorate? Do properly restored amps sound better?

Is an older unserviced amp more likely to go DC?

Does a stitch in time save nine? I mean, are you more likely to save yourself an expensive or even impossible repair if you get it serviced? 

Raging, rampant and unapologetic opinion here (based on 40+ years of noodling around the hobby):

Servicing SS (or tube) equipment ahead of catastrophic failure is generally a good thing. But:
a) What kills capacitors is lack-of-use. I keep a 55 year old Dynaco ST-70 that was used pretty much every day from the time it was new to the time I got it (11 years ago), and still has its original tubes but-for the 7199s which were very microphonic. The caps all tested good (ESR and value), the resistors had not drifted and so forth.
b) I also keep a Citation 16 and 19, both 'brute-force' amps in their way. The 16 had been used regularly, and was pretty much fine but for a LOT of cold-solder joints - something common in HK/Citation products, surprisingly. The 19 sat on a shelf for about 10 years with one channel out until I go it for chicken-feed. The bad channel turned out to be a cold-solder, but meanwhile most of the electrolytics were well on the road to failure. As I a NOT a believer in reforming, they were replaced outright.
c) I make a habit, for my sins, of restoring vintage Dynaco ST120s - solid-state amps that range from Glass-in-a-blender to quite sweet and stable. I don't even bother to test them, but I do the full TIP mod and cap mod upon arrival. They make excellent shop amps, test-bed amps and gifts-for-kids amps as when properly restored, they are bullet proof short of total immersion. And may be had often for as little as $10 in decent physical shape.

So, that covers the range:

A well-used, constantly used amp should have fewer problems than a shelf-queen.

Excellent circuit quality does not necessarily mean excellent build quality..

And about any good basic design may be salvaged and improved.

On protective circuitry - it depends very much on how it is done. Some amps use voltage-driven protective circuits that shunt out the power-supply, often via a Zener that clamps at a certain point - which means that if they are run at clipping but not quite enough to trip - they will pass excessive DC to the speakers. These, typically, are relatively early designs. But if you are concerned about straight B+ going into the speakers, that would take a number of failures in cascade fashion to happen - quite unlikely with a quality amp.

When an amp (pretty much anything) comes onto my bench, before it sees power, I will give it a detailed visual exam and sniff test. Then I will use a dental-pick to check solder-joints and look for anything loose or funny looking. Controls are cleaned, connections cleaned and so forth. Then I will apply power via a metered variac - much may be revealed this way. Failures, in rank order tend to be:

Failed electrolytic caps.
Drifted/open resistors
Failed small-value caps
Failed zener diodes
Failed diodes
Failed output transistors
Failed driver transistors
Anything else.

This is a hobby, so spending several hours to save a $20 item from landfill goes with the territory.

Peter Wieck
Melrose Park, PA