A while back I got some fairly acerbic feedback when I DARED to suggest that perhaps it would be a good idea to replace the old electrolytic capacitors in ham radio equipment. It was as if I had attacked motherhood and apple pie!
Yesterday I was looking at CuriousMarc's YouTube channel and I came across the above video. While I had been in the preemptive replacement camp, Marc makes a good case for leaving some of the old caps in place. The fact that the electrolytics usually are open when they fail, and that there are fuses in the power supply to protect the transformers, are important points. His admonition not to replace electrolytics with tantalum caps (which fail closed) was also very useful.
OK, my flame-proof suit is on!
A big consideration is that in the tube era, electrolytics were few. In the power supply, and bypassing the cathode of an audio stage or two. Maybe one elsewhere. Hum, or low gain, was the giveaway.
ReplyDeleteThat changed with solid state. Even the earliest transistor radios had more electrolytics. A change from high voltage low current to low voltage higher current. A bit harder to figure put which one is bad.
Switching supplies and comouters changed it again. No longer abput 60Hz, they were handling much higher frequencies. And often more complicated. Most hobbyists didn't understand switching supplies when they first arrived. So ESR meters became useful, especially to figure out which one was bad.
You don't need a flame-proof suit, you need flame-proof transformers. Fuses to protect them? Maybe, maybe not:
ReplyDeletehttps://www.instagram.com/p/Clh-aGfLI-O/
An ounce of prevention is worth a pound of burned-out components.
The collectors know about the troublesome capacitors.
DeleteSome good points in the video. My experience is in audio. Electrolytic PSU caps do not sit alone on a bench, rather they are part of
ReplyDeletea system which sees a load which typically varies over time.
Most professionals will measure power supply ripple with it connected to the typical PSU load seen in daily use.
A lightly loaded PSU usually behaves differently from 1 under heavy load; or a rapidly changing or transient load
PSU with bad caps may lag behind spec in situations of high slew rates and changing current. This in turn may affect noise and also performance if the caps are bad enough. Thus some. Some technicians will also consider slew rate and transient response.
Ripple may create noise voltage and that is the main reason to replace big aluminum electrolytic PSU caps in audio equipment.
Many data sheets specify a maximum peak-to-peak deviation of the output voltage caused by the ripple and noise and I check against that. By the way, I've seen caps fail open due to my friend Murphy and don't get me going about
the garbage caps that were installed in some computers and audio equipment in the 1990s or so. My experience is that some caps
just randomly fail and cause bad noises in the audio chain. Occasionally, when testing under load you may measure lower gain than expected for a given stage. These would be in cathode bypass or source/emitter resistor bypass capacitors and such.
Watch and learn from what Mr. Carlson does ;-)
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