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Peter Wieck[_2_] Peter Wieck[_2_] is offline
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Default Is it a good idea to get old SS amplifiers serviced if they still work?

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