Al - Do you remember to increase line voltage slowly over few days? Voltage re-builds up isolating layer of aluminum oxide in electrolytic caps, that tends to get thinner without voltage lowering breakdown voltage.
When is used used up?
Is there a rule of thumb that says the savings of buying used equpment is offset by the age of said equipment? Surely, aging negatively effects circuits -- welds weaken, capacitors lose capacity, transistors tire, wiring oxidizes, etc. My first amp in 2000 was a Mcintosh 250 in A- cosmetic condition. When I replaced it five years later with an HK PA2400 (used), my system took on new life (more than the increase in wattage).
Seems like when a component is old, it's old, be it sacred cow or not.
Seems like when a component is old, it's old, be it sacred cow or not.
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Hi Kijanki, Thanks for mentioning those things, but yes in my case I have absolutely always done that. During the 1990's I invested in an earlier version of this variable ac power supply. It provides a variac-type function that allows me to bring up the voltage slowly, while providing an ac current meter as well as a voltmeter. My standard practice is to bring up the voltage over a period of about 8 hours, rather than several days, and that seems to have worked well for me generally. The 50 capacitors that I mentioned I had to replace on one of the Scott's, btw, were all coupling caps, not electrolytics. I have, of course, had to replace electrolytics in other pieces of vintage equipment. Best regards, -- Al |
I have owned many old mac amps, and when I acquire them, I send them to Mac for general servicing. I have NEVER had them do anymore than replace a burned out lamp. Ever! And I am talking about amps and preamps that were 15 to 30plus years old. Each one met spec. The same is true when I bought my harman kardon Citation 17 preamp and 16A amplifier. I sent them to hk on Long Island and they sent them back with a data sheet. They far exceeded factory specifications. It erks me a little when someone says 'oh I replaced the caps in this or that and now the unit sounds awesome' (caps are so easy to change and this seems to be the rage today) Capacitors do NOT DEGRADE over time, they FAIL. Which means if your amp is playing, your caps are fine. So, I think that if a unit was manufactured using quality parts, you should be ok, at least that has been my experience. Norman |
"Capacitors do NOT DEGRADE over time, they FAIL." - I don't know where you got this from, but even capacitor manufacturers admit that electrolytic capacitors dry out (and rate them). At room temperature they will last for 30-50 years but temperature accelerates process greatly (each 10degC cuts life by 50%). ESR of capacitor increases over time and, in presence of big currents, causes internal self heating (just few degrees) and so forth. Power supply capacitor is in series with a speaker (circuit closes thru power supply) and any increase in ESR will show as worse bass control (lower DF) and loss of dynamics. We get slowly used to "new sound" but difference after replacement can be huge. There are electrolytic caps that are better quality, lower ESR, lower inductance (like slit foil caps) and higher temperature ratings but they are expensive. Better (high end)manufacturers most likely use better parts. |
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