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In Reply to: RE: In the circuit shown in the photo,... posted by Lew on June 17, 2016 at 10:39:59
Actual voltage is 75 volts. 16 is the number of 10,000 uF caps, half to each channel for the output stage. Amp is a tube hybrid with 6SL7 inputs (separate PS) and bipolar outputs putting out 220 watts / channel into 8 ohms and 400 into 4.
Edits: 06/18/16Follow Ups:
So choosing an 80V rated capacitor to filter a 75V supply is just about perfect. As the late great Gilda Radner said in her Emily Latella character, "Never mind".
voltage ratings. Some say to use caps that are rated 5 volts higher than the operating voltage. Counterpoint used to do and look at their failure rates in the power supplies too. Also this was the same in my EDGE amp that lead to a cap in the power supply failing. I used 100vdc caps where the power supply voltage was 50vdc. Still has that great sound my amp had before and my even bettered it.I always use capacitors that are 15, 20, or even 50 volts higher than the power supply voltages and same for rail voltages. I have never heard any difference compared to caps rated just 5 volts higher than the power supply voltage
I just want a longer lasting and safer unit. 5 volts under the caps rated voltage is too close for me.
Edits: 06/24/16
After I posted the above, I recalled that it was Kondo-san of Audio Note fame who is said to have expounded on this issue. Perhaps it was Art Dudley, or someone else of Art's stature, who re-stated what Kondo is said to have said. (Since I don't read Japanese, I of course have no direct idea what Kondo might have said.)
However, I don't recall anyone specifying a 5V margin; that IS cutting it close. The potential danger of going so close to the limit is that upon turn-on, in many types of gear, there is a transient voltage surge due to capacitors getting charged up. Probably not much of a problem in equipment using tube rectification or choke input filtering, but most modern stuff uses solid state rectification and capacitor-input filtering, where such a phenomenon does occur.
to it but I can't find it now. I was just commenting of what I had saw before and just wanted to let others know that this is not good.
I have seen in Counterpoint gear caps that were used in their power supplies with cap voltage ratings were only 5 volts higher than the operating voltages. a lot of those power supplies had damage due to cap failures.
I think I do recall there were reliability problems. Metallized film capacitors probably can tolerate a brief period of over-voltage better than either electrolytics or film and foil types. I am sure it varies according to construction and manufacturer's method of rating for voltage. Some are probably more conservative than others.
Quite a few of the problems were in the power supplies and with the caps failing and traces burning up. But they were great sounding gear and when fixed properly Counterpoint is some fine sounding gear.
The other issue was those tightly matched Mosfets that had no Source Resistors to share the current.
Counterpoint does have some of the best sounding Phono section in their preamps.
The other issue I found out was the Counterpoint gear goes through tubes faster than other tube gear I have. Maybe due to the way they are biased.
This amp bears no resemblance to earlier Counterpoint amps being a completely different circuit design. It has only a pair of 6sl7s for input and a separate toroidal choke regulated supply for the tubes. No funky tube matching issues like the old SA20. It uses matched bipolar output transistors not Mosfets with no resistors. All the parts in it are custom including the wiring and over 50 TX 2575s in the signal path and a giant custom Plitron power transformer for the output stage.Agree. Would not advise 80v caps on a 75 volt PS rail - using 100v on its twin. The muting relays minimize current surge on turn on. These particular PS caps have been in use for 15 years with no issues.
Sounds better than nice......
Edits: 06/29/16
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