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In Reply to: RE: It's not a mistake. posted by FenderLover on August 17, 2014 at 16:41:30
The schematic shows about +400V at that point. If that's correct, there's no reason the caps would need a 600V rating. You and I might build it that way, but I've seen factories do worse without adversely affecting product reliability. I'm betting they've had trouble with the 5AR4s. There have been some really poor quality copies (imports) of the original design over the last ten years. Fender probably found out the hard way that reducing the input capacitance was necessary to keep the more marginal examples alive. That's just a guess, of course, but I can't see any other reason for doing this.
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Buy Chinese. Bury freedom.
Follow Ups:
TK, when the amp is in standby the only load is the 570k ohms.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"when the amp is in standby the only load is the 570k ohms."
Yes, I see that now. So, maybe the voltage increase was more than the 500V cap alone could handle. It would be interesting to measure this on a live amp. In any event, I think FenderLover's idea to use two 80uF caps is reasonable. I'd probably use a pair at 330V, rather than 450V, just to be sure they stay formed.
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Buy Chinese. Bury freedom.
From the C-D manual and various other sources, it is fairly common (especially in military gear) to run electrolytics at less than the rated voltage to extend their lifetime. Usually this is done at between 50% and 80% of the maximum rated working voltage.
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Have Fun and Enjoy the Music
"Still Working the Problem"
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