| Re: K100-2 Hiss but no other output [message #21224 is a reply to message #21116] |
Wed, 20 August 2014 09:58   |
daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri
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Senior Member |
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Jerry:
Two things I always try to get changed first on any older piece of gear are the aluminum electrolytic caps, and especially any tantalum electrolytic caps.
The aluminum caps usually just dry out, the ESR goes up, and they usually just gradually stop working. Like your power supply caps getting weak. They can sometimes short, but that's far less common.
Tantalum caps are a different story. They can dry out, and just stop working, but their failure mode most often is to SHORT. If the cap is across the power supply as a filter, you can imagine the mess that can cause. If they are just in there to block DC, they suddenly start passing the DC they are supposed to be blocking, and can damage the following stages.
Tantalum caps are BAD NEWS! For the longevity of your amp, you really need to get rid of them all before they cause serious problems for you down the road.
You may be asking, why would they be used then.?. Well, they do very accurately hold their value over the long term...usually till they short. They are very good for timing circuits...like setting the repeat rate of your tremolo / vibrato. They were quite expensive back in the days these Kustom amps were built. It's not that Kustom was cutting corners, they thought they were putting in the best possible parts money could buy. We didn't know at the time that they would become so likely to short after many years of use.
BTW, tantalum caps are most likely to short when the amp has been sitting for a long time...like years, and then powered up. In daily service, they are not nearly as likely to short. I see this a LOT in older broadcast gear that has been sitting for years, then someone plugs it in, and the thing starts smoking, or catches fire!
Getting rid of all the tantalum and aluminum electrolytic caps in your amp would still be advisable. It will sound better, be quieter, be less likely to oscillate, and last a lot longer before the next failure.
I have very good results with the Panasonic FM series caps. They are rated for the higher 105 degree temps, are low ESR, and last a long time. I test every cap before installing it for value and ESR, and these FM series are consistently right on their rated value too...generally not more than +5%. That makes them pretty good replacements for timing circuits where tantalum caps were originally used.
Just my 2 cents worth,
Dave O.
Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >
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