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Can a 20 or 30 uF 160 VDC rated MBGO be safely used in a "slightly overvoltaged" state - as a higher quality bypass cap on an elevated Rk ?
( I am thinking of it operating at 180 to 202 VDC at the TOP of the Rk, in a direct coupled circuit. )
Anyone have experience with over voltaged MBGOs ?? Reliability ??
It would be a whole LOT cheaper than a Mundorf Silver Oil Gold there, for a budget build, and superior to a electrolytic.
TIA.
Jeff Medwin
Follow Ups:
We all know who has a basement full of them.
.
I wouldn't do so.
Cap life is dependent on voltage, temperature, and ripple. If you raise any quantity, lifetime can drop drastically.
Several capacitor manufacturers have papers and calculators on this topic that can be useful in making an informed decision.
There is absolutely no meaningful conclusion that can be drawn from a 160V cap running on 200V for a small period of time. You would likely lose at least 25% of the cap's lifetime, assuming the ripple and temperature aren't also eating away at things.
You're a fan of overkill, use four of those caps in series/parallel to get what you need.
For the Russian caps, if you look hard enough, the following data is available for the MBGO:
Max operating temperature: 70C
Lifetime rating (minimum): 10,000 hours (crap!)
If we plug that into a generic calculator, and we assume that your amp runs a little toasty at 50C, then you'll get 30,500 hours minimum in that position.
None of this takes the ripple current into account. I've had a 200V rated film cap explode from 60V DC applied across it and light driver stage ripple current levels.
Paul
I would normally agree and I only do that with the Russian Teflons that are 200v rated because they are clearly underrated being military.
Did you look at the rating on the 6P3S-E tubes that so many use? Those say 350v on the plate but we use them in Mc240s and Citation 5s and Heath W5ms,all which have from 420 to 450vdc on the plate. This is why I suggested he get the 400v ones because in the power supply with the surges you can get can go quite high..Military components are almost always application rated,meaning they rate then for a particular application.The military whether it be the US or the Russian,most run their components at about half of their rated potential for reliability.
Honest amplification is better than excessive 2nd order distortion anytime.
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.
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
Jeff
You will be fine to that voltage and I can guarantee you they will eat the Mundorfs for lunch..You can always get these.
Honest amplification is better than excessive 2nd order distortion anytime.
Edits: 09/17/14
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