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Tantlums
- Thread starter kaos513
- Start date
Tantalum capacitors do not go bad quite like regular electrolytics do. Personally I wouldn't bother unless there is a problem. In my 22 years servicing commercial broadcast gear I had ONE tantalum cap go bad. It was a bypass cap on a 600 volt supply rail and it went short.......well very low impedance and lit up like a lightbulb every time power was applied until the fuse blew.
I agree with Captain Kilowatt but will add that there is one place in our hobby you ALWAYS want to replace a Tantalum. Replace C179 (2.2uF. 25 volt) in any/all 858 sideband chassis. Replace whether it needs it or not with a .47uF or 1uF, 50 volt electrolytic.
Seconded. I've had one go boom inside a Cobra 139XLR, it gouged the underside of the metal top of the radio. Took a while to get all the little chunks out.
Dropped in an electrolytic as a replacement, radio has worked fine ever since.
When a tantalum cap goes bad, it's unpredictable. Unless some circuit stress is a clear cause. The one that goes bad in the Uniden-made uPD858 SSB radios is okay until the modulation is turned up. Not because it's a tantalum, but because it's only rated for 25 Volts. Calls for a 35-Volt or higher replacement.
Failure of aluminum electrolytic caps is far more predictable, due to the materials used to construct them. Age plus mileage makes them just wear out. A NOS electrolytic capacitor made in 1977 that was kept in the proverbial cool, dry place may very well check perfectly okay. But it won't last nearly 15 or 20 years once installed in a working circuit. Before long it will "remember" how old it is and fail even with low mileage.
And the ones we would see fail after only ten or fifteen years were usually in radios that ran 24/7.
73
Failure of aluminum electrolytic caps is far more predictable, due to the materials used to construct them. Age plus mileage makes them just wear out. A NOS electrolytic capacitor made in 1977 that was kept in the proverbial cool, dry place may very well check perfectly okay. But it won't last nearly 15 or 20 years once installed in a working circuit. Before long it will "remember" how old it is and fail even with low mileage.
And the ones we would see fail after only ten or fifteen years were usually in radios that ran 24/7.
73
Depending on the application it is used in an electrolytic may not be a suitable replacement for a tantalum. Tantalums are more stable and better suited for certain RF circuits than an electrolytic. Sometimes you can cause other issues by not using a tantalum. My SOP is to replace with the same kind of capacitor but make allowances for voltage rating or possibly value.
In the 50 years that I have worked on electronics, 45 of those for major corporations as an electronic tech only a few times did I ever have to change out a tantalum. The last company I worked for built equipment that has been running in their customers' facilities 24/7 since the mid 80's. Electrolytics,carbon resistors,transistors and ICs were the most common replaced items but hardly ever a tatalum. The most tantalums I have replaced that were bad have been C179 in the 858 chasiss. I used to pull tantalums years ago thinking they may be bad but after testing dozens of them from different types of radios and other electronic equipment and never finding any bad ones I gave up that practice.
Overall a good policy. If not for the rapidly self-disassembling C179 in the Uniden 858 SSB chassis I'd agree 100%.
Same here. And for the reason mentioned above. It's just not rated for more than 100 percent modulation in that radio.
73
