Should the electrolytics (esp. the big filter caps) in a 20 year old low bias class AB amp be OK? By low bias I mean runs pretty cool, not a lot of heat in the chassis interior to accelerate aging. I found an amp I've always wanted but it is 20 years old and not cheap ...
They probably are just fine. If the amplifier hasn't been used over the past decade, you may charge them slowly to reform them, although chances are that won't even be necessary (as it's not a 1950's tube radio that hasn't been used since 1970).
some electrolytics last decades others a couple of years. I bought 3 Kenwood power amplifiers a few years ago for less than $50 each. I bought them to use the chassis and power transformers for other projects. I bought 2 KM106 and 1 KM206. One of the KM106 was bad, I knew that before I bought it. The other 2 worked fine and tested fine. I am still using them. I believe they were made in the 1980's
Depends on the quality of the rubber seal of the caps. If you put them in, what service life rating did you buy? How many hours of use have they had? Wnt brand amp? Peavey amp e-caps are good for about 15000 hours, consumer grade amps 8000 hours.
You can test without a $120 ESR meter. Just a signal source, a set of speakers of known impedance, and a $30 analog VOM with a 50 vac or 20 vac scale. Check low ohms zero before impedance test, only perfect batteries can read below 10 ohms. Measure speaker resistance, multiply by 1.3 for impedance. Put analog VOM leads to speaker terminals with alligator clips. Turn music up until it sounds funny (clipping) then back off slightly. write down AC volt reading. Read other channel and right down . Takes music in both channels to stress mains caps to the max. P=(V^2)/Z . Add the powers of both channels. Measured power = rated amp power, your mains caps are fine. Measured power < rated power, your mains caps are likely at fault.
Reason for analog VOM, my $40 digital DVM produce random numbers on music. Other british posters bought the right DVM that doesn't. Everything is better in the UK. AndyG UK moderator of organ forum has never needed an electrolytic cap replaced. I've replaced about 400 of them. 4 times my ST70 went low power.
If you don't want to do this every 8 years or 16000 hours, buy ecaps rated >3000 hours service life. Or don't ever turn your amp on. Digikey & Newark will show you the rating of the e-caps they sell. Mouser makes you look up the datasheet & read it.
You can test without a $120 ESR meter. Just a signal source, a set of speakers of known impedance, and a $30 analog VOM with a 50 vac or 20 vac scale. Check low ohms zero before impedance test, only perfect batteries can read below 10 ohms. Measure speaker resistance, multiply by 1.3 for impedance. Put analog VOM leads to speaker terminals with alligator clips. Turn music up until it sounds funny (clipping) then back off slightly. write down AC volt reading. Read other channel and right down . Takes music in both channels to stress mains caps to the max. P=(V^2)/Z . Add the powers of both channels. Measured power = rated amp power, your mains caps are fine. Measured power < rated power, your mains caps are likely at fault.
Reason for analog VOM, my $40 digital DVM produce random numbers on music. Other british posters bought the right DVM that doesn't. Everything is better in the UK. AndyG UK moderator of organ forum has never needed an electrolytic cap replaced. I've replaced about 400 of them. 4 times my ST70 went low power.
If you don't want to do this every 8 years or 16000 hours, buy ecaps rated >3000 hours service life. Or don't ever turn your amp on. Digikey & Newark will show you the rating of the e-caps they sell. Mouser makes you look up the datasheet & read it.
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