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 Post subject: electrolytic cap voltage question
PostPosted: Jul Thu 22, 2004 10:50 pm 
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Location: Lincoln, NE
I am working on a Philco 38-7 radio. One of the original electrolytic caps has a 475 volt rating. The highest that I have are 450 volts. Do I need to find one that is rated higher than 450 volts?<BR>Thanks,<BR>Jason<P>------------------<BR>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 12:22 am 
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Location: Circleville, OH, USA
The 475 was usually the surge peak rating. This is the voltage the cap will be exposed to as the set warms up - not the operating voltage. A modern 450V cap should work OK.<P>------------------<BR>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 12:31 am 
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Go ahead and try a 450 V cap. Best to check the voltage on it as the set warms up. If the voltage goes over 450 V for a few seconds during warm up, it's OK, as long as it's not way over (like 550 V or more).<P>For maximum capacitor life, operating above the rated voltage, even for relatively short times, is probably not the best. However, it will still probably work fine for several years.<P>If you find that the voltage doesn't exceed 450 during warm up, then you're in pretty good shape.<P>Some people recommend having a lot of voltage margin between the cap rating and the voltage in the circuit. This extends the capacitor's life. However, it's hard to find electrolytic caps with ratings higher than 450 V (although 500 V caps are available from a few sources).<P>Tom<P>------------------<BR>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 1:01 am 
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Hi Jason<P>Like Ken and Tom mention, a 450V "should" be OK. An E-cap rated at 450 Volts would have a surge rating of aprox 550V. Although 450V is by far the most commonly needed voltage for AC tube radios .... 475V is specified for a number Philco models and some other brands/models even call 500V. If you want to "play it safe" (and don't mind spending an extra $ dollar on your radio restoration) you may want to use a 500V. We stock 500V axial ecaps at 10mfd, 20mfd and 40mfd at <A HREF="http://www.justradios.com/capacitors.html" TARGET=_blank>http://www.justradios.com/capacitors.html</A> AES also carry 500V Ecaps.<P>Regards<BR>Dave (of JustRadios)<P>------------------<BR> <A HREF="http://www.justradios.com" TARGET=_blank>www.justradios.com</A>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 2:04 am 
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You'll find 500-volt electrolytics from most mail-order vendors. I strongly recommend using them if the original part was rated 475 volts. They didn't do that without a good reason.<P>The surge rating on electrolytics is the peak voltage for one half-cycle, non-repetitive. Since the voltage in a tube radio can stay high for several seconds while the tubes warm up, it definitely exceeds the surge spec of a 450-volt cap.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 2:32 am 
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May not be a bad idea to keep a few 500 volt caps in stock. I`m going to eventually order a few.<BR>I generally use 450 volt. I`m not sure what I am getting with these 450 volt getting smaller in size.<BR>Maybe its just me.<P>------------------<BR>Rodney


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 2:59 am 
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Hi Rodney,<P>I stock half a dozen 10 mfd @ 500 volts. I do use them fairly often.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 3:04 am 
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Hi Jason<P> The schematic shows voltage at your 5Y4 rectifier is 315. Voltage out of a rectifier, under load, is usually close to AC on the plates. <P> If AC on the plates is 315 then no load voltage out of your rectifier can reach 445 volts. (315 x 1.414) This voltage goes down when other tubes heat and start drawing current.<P> Seems safe for a 450 volt electrolytic but what is the AC line voltage? Philco got a reading of 315 with the line at 115. With 125 volts input it will increase to 342 volts. No load peak voltage could reach 483. (342 x 1.414) <P> Electrolytic caps can withstand a peak voltage over their rating. If the speaker field was disconnected voltage would stay at the no load peak on your first filter cap.<P> <P>------------------<BR>Norm


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 5:06 am 
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I`m thinking the 500 volt would offer a little insurance policy in some situations.<P>------------------<BR>Rodney


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 3:01 pm 
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When I saw this trend, I went to my PHILCO schematics and sure enough PHILCO stated this in 1938, but PHILCO did a lot of things with voltage ratings, like 1000-volt caps, that no one knows why!<BR>I agree with Norm, I don’t see a problem<BR>Just 10 mfd huh Leigh, so if it’s anything else you just order them?<BR><P>------------------<BR>Rick Dippolito<BR>THE PHILCO RESTORER at<BR> <A HREF="http://hometown.aol.com/philcorestorer/myhomepage/index.html" TARGET=_blank>http://hometown.aol.com/philcorestorer/myhomepage/index.html</A>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 3:34 pm 
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Hi Rick,<P>The original caps were in the 4 to 8 mfd range, so 10 seems like a good value to stock.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 5:45 pm 
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What about 2 15 mfd 450V electrolytics in series with 47K resistors in parallel to each unit? This will give 900 volts rating.<P>------------------<BR>


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 Post subject: electrolytic cap voltage question
PostPosted: Jul Fri 23, 2004 6:42 pm 
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Leigh wrote:
<font>quote:</font><HR>Originally posted by moe cory:<BR><B>What about 2 15 mfd 450V electrolytics in series with 47K resistors in parallel to each unit? This will give 900 volts rating.</B><HR>
<P>Hi Moe,<P>That will work. I would use 470K rather than 47K, but it doesn't matter that much. Probably want 1-watt resistors.<P>------------------<BR>73 de Leigh W3NLB | | Leigh@AtwaterKent.Info<BR><A HREF="http://www.AtwaterKent.info" TARGET=_blank>http://www.AtwaterKent.info</A> | | <A HREF="http://www.Synchrophase.info" TARGET=_blank>http://www.Synchrophase.info</A>


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