A couple of years ago I was in the market for a good, but used, Mark Levinson 585 Integrated amplifier. As part of my research I looked for posts on how to determine if capacitors need to be replaced.
I copied and saved relevant Audiogon comments I collected on buying a used amplifier; I hope you find them useful:
- Depending on the unit’s age you may be looking at replacing all the capacitors in the circuit, and this could prove expensive. But it’s worth doing to optimise reliability and performance, particularly if you intend to use the product for a while. Other internal components will tend to have far longer lives and aren’t worth worrying about.
- Usually the electrolytic power supply caps will start to go first, which will cause a hum through the speakers.
- Worn capacitors will result in an amp with an increase in noise or hum, possible ghost notes and a definite deficiency of punch and low end. Often times the capacitor will bulge, or leak when they wear out. Other times an amplifier will have a pulsating-type oscillation known as “motorboating”. This is another sign that the time has some for the electrolytic caps to get replaced.
- If a filter cap is going bad, you can hear a lot of buzzing, including but not limited to 60Hz. If you actually look at capacitors inside the amp (do not touch, even when unplugged!) they can appear to be deformed, bulging out at the ends, etc.
- Generally its only electrolytic capacitors that need replacing, the most critical being the ones serving as filters in the power supply.
- If the amp has seen moderate regular use over time the caps may last longer - if its been gigged regularly or been sitting for long periods probably needs service sooner - kind of like a car.
- 10 years for filter caps seems to be common wisdom - if there is such a thing. Capacitors may last 30 years - what u are doing in replacing them every 10 years is avoiding the potential of catastrophic failure.
- If an old electrolytic shorts, you hope the fuse goes before the PT winding...chance you take. If they internally leak current, they will pull more current through the PT making it run warmer and will likely lose some of their filtering capability causing the amp to hum in varying degrees. If they open, the amp will hum badly.
- it's the filter capacitors in the power supply that go bad generally, and the ones that can do some additional damage. Electrolytics officially have a shelf life of around a decade. However, they last longer if installed and charged/discharged regularly. A lot of people will replace them at 20 years, just as a precaution. It's not going to hurt anything and not terribly expensive.
- Listen at a fairly loud volume, and if you hear buzzing, hiss, crackling, pops, distortion, fuzz, or anything that sounds off, don't buy it
- Listen out for any unexpected noises when you work the volume, tone and balance controls, as well as any switches.
- Reject those with scratchy sound or crackles that indicate dirty or worn controls.
- Listen for hiss and background noise from amplifiers and pre-amplifiers with the volume set very high and no program playing. Do this with the controls set on "phono" and then on a "line" input. Put your ear right next to the loudspeaker. If all you hear at maximum volume is silence or a slight rushing noise, they pass the test. (Phono will always be noisier than a line input.)
- With music playing, rotate the tone and volume controls to insure that they track correctly, with no dropouts or sudden volume changes that might indicate worn potentiometers.
- open the case and visually check the parts inside for leaky capacitors, burned resistors, cold or corroded solder joints and chassis rust.
- A well-cared for transistor amp of good design and built with good parts should last and last and last. Of all electronic components, an amplifier is the only one I'd consider buying used.
- The only thing that wears out are the electrolytic caps in the power supply. They dry out over time. Their lifetime shortens exponentially with temperature so the higher temp you operate your amp at the sooner they will die.
Good luck!