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R34 & R35 Panasonic ERX vs ERG

beta22

R34 & R35 Panasonic ERX vs ERG

Postby fishski13 » December 3rd, 2012, 8:35 pm

the part number under the Part List for the Panasonic ERG2S from Digikey, P0.47W-2BK-ND, yields the similar ERX: http://www.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=+P0.47W-2BK-ND. while looking through the datasheet it appears that they are the same, but the ERX is a "metal film" and not "metal oxide". the ERG series doesn't come in values lower than 10R. does the ERX behave as the metal oxide ERG wrt increasing resistance in the event of a short?
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Re: R34 & R35 Panasonic ERX vs ERG

Postby amb » December 3rd, 2012, 11:12 pm

Typically metal film types reduce resistance when overheated. This is opposite that of metal oxide. Interestingly, according to the Panasonic datasheet (and Digikey's current online catalog), the ERX2SJR47 is metal film, but I've ordered these from Digikey before and the package label says "metal oxide". The latter is probably wrong:

ERX2SJR47.jpg

At any rate, search Digikey for ".47 ohm 2w metal oxide resistor" and you'll see suitable alternatives from Stackpole and Yageo. I'll change the parts list to reflect this latest finding.
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Re: R34 & R35 Panasonic ERX vs ERG

Postby xt0rted » January 12th, 2019, 9:05 pm

After 8 years I've finally started working on my β22. Upon reviewing my resistors for R34 & R35 I found that I had some Vishay Metal Film as well as the Panasonic ERX Metal Film.

I then checked the σ11's for my M³ and γ2 and those look to be using the Panasonic ERX metal films which were on the parts list back when these were built. Both of these have been running for over 8 years now without any issues.

I guess when I ordered my β22 parts I got the Vishay equivalent of the Panasonics not realizing I had extras already, or that neither was actually metal oxide. Should I pass on using the Vishay & Panasonics that I have and get new from Xicon or Stackpole? What about my two σ11's, should I order new for these as well and swap them out?
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R34 & R35 Panasonic ERX vs ERG

Postby amb » January 12th, 2019, 9:25 pm

Metal oxide resistors, when overheated, increase in resistance. When severely overloaded they burn up into an open circuit, sort of like a fuse. This property may protect the MOSFETs (on both the amp board and power supply) from collateral damage under some failure circumstances.

Metal film resistors have the opposite behavior, and may make a situation worse.

Whether to replace the metal film resistors with metal oxide is up to you. Under normal operating conditions there is no difference.
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