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 capacitors voltage rating
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 12th July 2006, 01:45 PM #22 diyAudio Member     Join Date: Jun 2002 Location: Left Coast Since cap voltage ratings come in discrete steps precise calculations are not really needed. A simple ruke of thumb from the "belt and suspenders" crew is take the nomina rail to ground voltage and select the next higher cap rating that is at leat 20% greater. Example it the rails are +35/0/-35 use two 50V caps. For +42/0/-42, 50V is just a tiny bit low so use 75V or 80V. Etc.
 12th July 2006, 01:54 PM #23 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Hi Sam, have you time to edit that 50V to 63V? __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 12th July 2006, 02:41 PM #24 diyAudio Member   Join Date: Jan 2006 Location: Trondheim Yes, I have measured the voltage with 230 on the primaries from a variac. This is the same as the nominal in the house mains. The secondaries measured 46v on the recifier with no capasitor. With a capasitor I stopped the primary at 215 with a 0.2ohm power resistor in series with the + and one 66000uF capacitor. The voltage was then 58v. I was hoping that a 1,5 ohm resistor would bring down the voltage with about 6v and just below 60v. The spikes in the net should be kept below 75v and therefore I should manage these. There is obviously something that I have not thought of. Please help me get this right! My part supplyer ment that by using resistors on the secondaries would help me bring the voltage below 60. He has built Alephs, but I don't know if he has used 60v capacitors. I need to get this to work....soon....! Tnx for all the help!
diyAudio Member

Join Date: Jun 2002
Location: Left Coast
Quote:
 Hi Sam, have you time to edit that 50V to 63V?
That's what happens when you write on the fly. Same idea, though, you only have a few finite choices.

diyAudio Member

Join Date: Jun 2002
Location: Left Coast
Quote:
 Hi Sam, have you time to edit that 50V to 63V?
That's what happens when you write on the fly. Same idea, though, you only have a few finite choices.

Before getting involved in the hobby, I thought electronics was more precise. At first I marvelled that 100, 1k, 10k etc were so often just exactly the required resistace value.

 13th July 2006, 07:17 AM #27 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Hi, My most accurate tool is a straight edge with a straightness tolerance of 0.01% Electronic components can easily match or better this. However good design allows adequate performance from a sensible spread of production values. Electronics is a precise art, when you want/need it to be. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 13th July 2006, 07:01 PM #28 diyAudio Member     Join Date: Jan 2004 Location: So Calif. For what it's worth... In 1992 I built some Synder based Krell mono blocks. The loaded rails were 53 volts and the unloaded circuit was 58 volts with a CL 30 (5ohms) on the line. I used 59,000 uf caps at 50 volt 63 volt surge ratings. In no way am I reccommending this is a good idea, but since I had them on hand at the time and couldn,t find anything with that much mfd at a higher voltage... well a few beers later and a gun to my head.. just do it!..--- They lasted 12 years before they needed replacement--- (This was indicated by hearing a soft crackling distortion in one amp) This is when I pulled them out and replaced them. Their ratings are conservative enough (based on my experience only) that a little gambling was in order since tring to find big capacitance at higher voltages is always tough at DIY prices. Regards David

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