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question for Michael Samra

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Posted on March 12, 2017 at 10:41:42
gkargreen
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Hi, Michael, I recall seeing a post a while back that indicated that the Russian PIO caps were a good bit under-rated regarding their voltage ratings. I was wondering if that is true of both the K40y and the K42Y caps. Also, do you have any experience with the Russian MBM PIO caps that are showing up on ebay? Thanks, Randy

 

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RE: question for Michael Samra, posted on March 12, 2017 at 12:18:52
Michael Samra
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Randy
The K40-Y and k42-Y caps you can over 50vdc but I wouldn't go anymore than that.The Vitamin Q caps are ones you can go higher with but I don't do that anymore either.The reason I don't is because of turn-on voltages which come up to the source voltage many times. The MBM caps I would stay the hell away from.Those are a dry paper cap that isn't sealed and they always leak DC and can short out at even half of their rated voltage.

The cap you can go way over the rated voltage are the Russian Teflon FT2s and FT3s. The 200v rated ones I used in 600v applications all the time.Having the wonderful Sencore LC102 capacitor analyzer has allowed me to see the actual break down voltage on all these caps and in the case of the FT2s,it is over 750vdc.Keep in mind that when you replace a 630v cap,it doesn't mean the cap sees 630v across the cap.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: question for Michael Samra, posted on March 12, 2017 at 13:44:56
gkargreen
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Thanks, Michael, that is all go to know. Since space is a concern in these old Scotts & Fishers, etc., I often use the voltage values on the schematic and measured in circuit to determine the voltage rating of the caps I replace with. For example, if the plate is only seeing 150 volts, a 250 volt CDE film and foil, which is much smaller that the 400 volt ceramicaps in the Scotts, gets used as it saves space.

 

RE: question for Michael Samra, posted on March 14, 2017 at 10:55:29
Michael Samra
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The K42s are smaller and they have higher voltages as well.The original Radionic caps in the Scotts are also a film and foil and they are an excellent sounding cap when they work. You also want to use a K40y or an FT-2 in the integrated amps going from driver to output tubes.I also like to use a paper in oil from the phase splitter to the driver.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: question for Michael Samra, posted on March 14, 2017 at 11:46:22
gkargreen
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Thanks for the suggestion, Michael, I am looking to get some the FT-2 caps and try them out, you suggested that the 200 vdc ones are good to 600 vdc? It appears that the radionic caps in the Scotts have a high failure rate, particularly the output couplers and the voltage/PI couplers, I am just replacing them as a matter of course with CDE film/foil (DMM and other types, not the metallized foil) and/or k42y/k40y where I have space, also using the Sprague 716 film/foil.

 

Take a look at a test I did on the different capacitors., posted on March 14, 2017 at 13:18:59
Michael Samra
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The FT-2 shows zero leakage at 765vdc.That is remarkable.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Take a look at a test I did on the different capacitors., posted on March 14, 2017 at 14:31:12
gkargreen
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Thanks, Michael, were those the 200 vdc FT2's?

 

Michael, what about the K73 caps?, posted on March 14, 2017 at 17:33:53
gkargreen
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these are noted as PETP type, thanks!

 

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