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In Reply to: RE: Russian MBGO .... Question..... posted by Michael Samra on September 18, 2014 at 15:10:42
Mikey,
Running a Russian Teflon over its rated voltage will decrease its lifetime. We just don't know how quickly their demise is accelerated by doing so.
Military ratings for resistors, for example, are still too high IMO.
I have seen resistors that carry separate power ratings for military use and commercial use. I have not seen this for capacitors and voltage.
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Paul
You can't fit the larger teflons in some applications and the sellers that sell the teflons over in Ukraine and Russia said the caps are good to the higher rated voltages but they didn't say this about the k40s..If you look at the .1 at 200v teflons,they are about the same size as the 600v ones but just not quite as big around..I have been using them for six years in several amps and preamps that had 400v and 600v rated caps and not one has failed yet..Then again,they don't really see 400v or 600v except maybe on warmup for a few secs.
The military rates everything at about 50% potential value..I have a friend that was an E9 Sargent in the Navy and he repaired radar systems and big Colins HF radios and encryption gear and he is the one that told me about this...I asked them if the Russians did this and he told me not only the Russians do this but so did the Brits.Reliability is paramount and they are constantly testing components for that reason..He also told me that all equipment had to have domestic made parts but that has changed in the last 10 years tho..
The teflons are real tough caps and you cannot rip that teflon apart by hand....I have a Sencore LC-102 and you can put up to 1KV on the caps you test and then you read the leakage.The FT2s did not show any leakage at just over 700v however it did start climbing once you got to 730 and then at 768vdc I leaked less than 8mv.That is pretty dang good for that much voltage and I left on over night but I put a 100k in series with it to limit the current..That cap was still cool in temperature...I'm convinced.
Honest amplification is better than excessive 2nd order distortion anytime.
Edits: 09/18/14
I tested many capacitors for leakage over time using high voltage. The Russian capacitors are typically over- built. I operate K40Y-9 at rated voltage and have no issue of over-voltage during tube warm up time. Never found or had a K40Y-9 failure. The K40Y-9 does not leak more than two micro amps at 1.5x the rated voltage or well within safe operating parameters. Same goes for the Russian Teflon capacitors. Where room exists, I do prefer some voltage reserve though.However, the subject capacitor MBGO is not a K40Y-9 or Teflon. Some faulty NOS MBGO exists. Measure the resistance across the MBGO. Bad caps will show as low as 200K ohms. Others measure in the 10+ meg ohm range. I would not have an issue using up to 200 volts on a MBGO measuring 10+ meg ohms. If this application was NASA flight critical though, I would be 'out' for sure.
Edits: 09/19/14
Excellent info.
Honest amplification is better than excessive 2nd order distortion anytime.
Thanks, I do MBGO resistance checks as per your information. Very good !!
Jeff
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