Tantalum Caps VS Electrolytics

[HavaV10]

I have a Cobra 2000 GTL I just finished recapping all electrolytics on the main board. Now from what I have heard and read is that the tantalums should be changed out also before failure. My question is has anyone swapped out all the 12 tantalums for electrolytics in the Cobra 2000 before?

 

[Cable Guy]

I do, but some only replace them if failed. They dont come in a recap kit so you will need to order them. As I understand, when tantalums were in their infancy, they were prone to failure due to manufacturing processes and electrolytic composition. I don't know what years that timeframe includes, so I replace them on anything pre 90s as a course of habit. Maybe I'm wasting time as I don't see them failed as much as I expect, but no harm.

Edit, that's a nice radio btw.

 

[HavaV10]

I do, but some only replace them if failed. They dont come in a recap kit so you will need to order them. As I understand, when tantalums were in their infancy, they were prone to failure due to manufacturing processes and electrolytic composition. I don't know what years that timeframe includes, so I replace them on anything pre 90s as a course of habit. Maybe I'm wasting time as I don't see them failed as much as I expect, but no harm.

Edit, that's a nice radio btw.

thanks for your input, radios works fine. I'll just leave the 12 tants in there.

 

[Captain Kilowatt]

thanks for your input, radios works fine. I'll just leave the 12 tants in there.

Tantalum caps have a much better thermal stability than electrolytics and are prefered in some situations because of it such as oscillators etc. I would not simply sub out and replace them with a regular electrolytic unless they were simply in a bypass or audio series feed application.

 

[Handy Andy]

+1 to @Captain Kilowatt comment.

Tantalum's in recent years - the quality has changed as well as their sourcing - which also changes their response characteristics you've come to expect in the early model radios - simply by their Audio response.

Just head over to a Guitar center or any music store of recent vintage - they may have the latest in compressor technology but open them up you will be gently surprised that they kept many of the older system filters - still using those ranges of values, design and composition just to keep the sound reproduction for the ones that use this performance equipment as expected - it's the only way they stay in business.

• There is an interesting debate about the use of Germanium Diodes versus the Schottky. There are benefits and drawback - the designs of both - one tends to favor the reproduction aspects and performance of Germanium that Schottky cannot truly reproduce faithfully even with filtering.

The main audio line - as you work with these Base radios and several of the higher-quality level mobile radios - they used Tantalum's in the audio path and in-and-around the audio chip sections - for their reliability and tolerance and their ability to provide a working level of performance in such environments.

You can throw in a Electrolytic but when you get down to the level of quality you want to have, the tantalum gets swapped back in - in some cases their performance curve is the only way a radio will work and sound like it does.

You did ask a valid question about their quality - I have yet to locate a bad tantalum - very few have gone bad, and most of the time it's a physical failure - not internal. Tantalum even as a ceramic material - they still have an MUF-limit - the use of them in RF circuits is somewhat limited - they work best with audio impression - like AM and FM audio processing and development while even though repackaged as "chip" SMD - they still don't truly reproduce that which their discrete bretheren do - per packaging.

 

[TM86]

The only tantalum I routinely swap out for an electrolytic is C179 in the uPD858 chassis. That's because that particular cap has a history of highly energetic spontaneous disassembly. Other than that, no.

 

[HavaV10]

ok thanks everyone for your input. I really appreciate it.

 

[nomadradio]

a history of highly energetic spontaneous disassembly.

C179 breaks down not because of age alone, but because of its 25-Volt rating. If the AM modulation remains factory stock, C179 should last a long time. But as soon as you turn it up, the audio peaks coming out of the modulation transformer will exceed 25 Volts and kill C179 from over voltage stress. C179 should always be replaced with a 35-Volt or higher cap.

73

 

[HavaV10]

C179 breaks down not because of age alone, but because of its 25-Volt rating. If the AM modulation remains factory stock, C179 should last a long time. But as soon as you turn it up, the audio peaks coming out of the modulation transformer will exceed 25 Volts and kill C179 from over voltage stress. C179 should always be replaced with a 35-Volt or higher cap.

73

so this is on the cobra 2000 board your speaking of? If so I will get it replaced with a higher voltage value.

 

[nomadradio]

No, this is for the 1978 Uniden-built 40-channel SSB radios with the uPD858 PLL chip. That circuit board was used in a variety of brands and models. All of Uniden's later SSB CB circuit boards are free of this fault.

73

 

[doffo]

C179 breaks down not because of age alone, but because of its 25-Volt rating. If the AM modulation remains factory stock, C179 should last a long time. But as soon as you turn it up, the audio peaks coming out of the modulation transformer will exceed 25 Volts and kill C179 from over voltage stress. C179 should always be replaced with a 35-Volt or higher cap.

73

Always appreciate your input on stuff. It was a few years ago when I seen that video that MikesRadioRepair did and mentioned that C179 tantalum cap. I wasn't sure if the generic tantalum caps you buy off eBay was worth risking it, so I just bought some Vishay branded ones.

 

[nomadradio]

Vishay branded ones.

A safer bet in the age of fleabay chinesium.

73