Does the quality of fuse vary for a given rating? I am asking the question in terms of the fuse's function not in terms of sonics. That is will some fuses provide better protection than others despite being the same type, say slow blow, and rated the same?
I blew all the rail fuses in my RB-1080 amp, but didn't know it. Put it into the shop, ListenUp in Denver, and they treated me right. Told me what was wrong, replaced the blown fuses and tighten everything up, tested it out, etc. I brought it home and it ran fine for about 3 months, then the rail fuses blew again. I replaced them with slow-blow fuses and have not experienced a blow-out since. That was 2 years ago. The RB-1080 blowing rail fuses is a known issue. Some A'gon'rs have posted that replacing fast-blow fuses with slow-blow is risky for your speakers, because the amp is allowed to pump more current into them before the fuses blow, but I haven't had any problems.
Fuses are incorporated in the design of equipment to protect critical parts against excessive current. A blown fuse can result from abnormal electrical surges or from issues within the equipment itself. I would contact the manufacturer if I had equipment that was frequently blowing fuses.
Regarding the type of fuse, most of my amps have come with fast blow fuses. One amp designer told me, in their opinion, slow blow fuses were not "as linear" as fast blow fuses so they did not believe the slow blow fuses to be as good sonically.
Regarding quality, the past few years have seen several manufacturers using different (improved?) materials in their fuses, from gold end caps, to ceramic bodies, and even different metals such as silver or copper for the filament. I suspect the connection of the fuse to the circuit board could also have some effect on sonics. Some folks wrap teflon tape around the fuse or around the fuse and connection tabs to dampen resonances. Manufacturers of "high end" fuses include HiFi Tuning, Isoclean, Furutech, PS Audio and others. As an example, the PS Audio "Critical Link" fuse offers the following;
Direct gold plated end caps OFC copper end caps OFC copper fuse element Foam damping inside Cryogenically treated
One amplifier designer/manufacturer I know has high regard for the Furutech fuses on a sonic basis, and uses them in amps and preamps, even though they only come in a slow blow type. Another rather large manufacturer of high end gear told me within the past year they had not yet concluded how to approach aftermarket fuses with regard to equipment repair and warranty, and they had some concern that not all the aftermarket fuses were properly constructed from the standpoint of protection of the equipment. I found that an interesting comment.
My question is not regarding the sonic capabilities of audiophile fuses but is specific to standard fuses and their protective capacity. After all there is the ongoing thread "fuses that matter" that is debating the topic of the sonic capabilities of fuses to death.
The reason for my question is that I recently blew a fuse on my power amp (tube amp). I replaced it with a standard fuse that was rated the same the stock one (2a slow blow). It was purchased from electronics parts distributor. when comparing the new fuse to the stock fuse, I noticed that new one was constructed flimsily. But both were rated the same.
After replacing the fuse while adjusting the bias I shorted one of the output tubes. I immediately shutdown the amp and upon inspection of the fuse it is unclear as to whether it failed (as it should have) or wether it survived the incident. This has prompted me to worry that maybe the fuse had something to do with the shorting of the tube. It is clear to me that the tube in question was nearing the end of its useful life, therefore causing the stock fuse fail in the first place. Regardless, if the tube was faulty the new fuse should have failed as the stock one did.
@Realremo, is changing the fuse type from slo to fast blow wise? I am not convinced, if the circuit was designed with a given fuse type I am not comfortable second guessing the design.
One small side bar regarding the rating of the fuses, engraved on the fuses are the following markings:
stock fuse: buss 250v 2A MDL CSA / UL (logos)
New fuse: CQ 250v 2A ADL CSA / UL (logos)
Does anyone know if these marking have any bearing. Most specifically the MDL vs ADL designations?
I'm not an electrical engineer, the are much smarter people on this forum than I, but it seems to me that replacing a slo-blow with a fast blo fuse presents less of a risk than vice versa. The fast blo fuse should fail faster than a slo-blo, which would mean less risk of voltage spikes throughout the remainder of the circuit. I would definitely try to obtain fuses with identical markings tho. I just went to rat-shack and the guy there selected the slow-blows for me, i brought my blown fuse with me and told him I wanted a slow-blow version. I also scoured the internet and found a list of approved fuses deep in the innards of the Rotel site. it was a spreadsheet of fuse types per amp.
I suspect that the original fuse was a Cooper Bussmann MDL-2-R, for which the manufacturer's datasheet is shown here. Does that appear to be correct?
And what is the manufacturer's part number of the replacement you ordered? That number should be indicated on the catalog page of the distributor you ordered it from. It should then be possible to find the manufacturer's datasheet for that part number, and compare the technical specifications of the two fuses.
Without comparing the specific technical data, I don't know what the differences are between the MDL and ADL series. Based on a quick search, I couldn't find any relevant information about ADL types.
To address the more general questions, the major manufacturers of standard fuses, such as Cooper Bussmann and Littlefuse, provide detailed technical info in the datasheets that are available at their websites. I haven't had occasion to make any comparisons between their specs for similar fuse types, but I would expect that for similar fuse types made by the major manufacturers some spec differences would exist, but they would be minor.
I would not expect the same to necessarily be true in other cases. I have seen a number of posts here in the past indicating that users have found some Radio Shack slow blows to act more like fast blows. And concerning audiophile-oriented fuses, I second Elizabeth's earlier comments.
Concerning substituting slow blows for fast blows and vice versa, obviously substitution of a slow blow for a fast blow will compromise protection to some degree, while substitution of a fast blow for a slow blow may result in frequent blows that are unnecessary.
While there are a number of differences between the specs for the two fuses, I don't see anything all that dramatic. Although the Conquer ADL datasheet is not nearly as comprehensive as the Buss MDL datasheet.
The Conquer ADL has a nominal melting spec of 48 amps squared-seconds. The corresponding figure for the Buss MDL fuse is 62.3, which would suggest that the ADL will blow a little bit more readily. However, those are nominal (typical) figures, and each fuse can be expected to have a fairly wide tolerance (range of variation) about those numbers. Also, the specific test conditions are not indicated in the case of the Conquer fuse.
Both datasheets provide figures for min and max blow times at 200% of rated current (which would be 4 amps in this case). Those numbers are 5 seconds min and 120 seconds max, for both fuses.
"Interrupting ratings" are 100 amps at 250 VAC in both cases. Cold state resistance is spec'd a little higher in the case of the Conquer ADL fuse, but the ADL datasheet doesn't indicate what current level that is measured at, so direct comparison is iffy. And that number doesn't have much if any relevance to protection anyway.
That covers essentially all of the relevant specs that are provided in the ADL datasheet. The Buss MDL datasheet is more comprehensive, as I said, so a fully conclusive comparison can't be drawn. And who knows how accurate the specs are? But based on the info that IS provided on the ADL fuse I don't see any worrisome differences.
Al, I guess that answers my question, there is little difference between fuses manufactured by reputable companies. At least as applies to the two brands in question.
I will rest easy knowing that damage done to my amp had nothing to do with the fuse selection. And, I will be far more cautious in terms of checking my tubes if a fuse ever blows again.
Thanks again.
@Marakentz the nice thing about Wiki is that if the information is missing or is not to your liking you can always add or change it. I look forward to learn about fuzzes!
Nick_sr, Your thread here, plus a little down time for minor surgery, got me looking further into the whole fuse thing. Here is a link with some interesting reading posted by the Roger A. Modjeski, the designer of Music Reference amplifiers. http://www.audiocircle.com/index.php?topic=105425.0 Another interesting post is located down near the bottom of the same page by Scott Novak, which starts out...
After having spent 6 years performing safety testing on switching power supplies I would be very concerned about using any protective device, fuse or circuit breaker, that did not have safety agency approvals.
Update, I got my amps back from service this week, it turns out that only the led for the bias adjustment was fried. So I guess the fuses served their purpose after all.
I would also like to take this opportunity to thank Quicksilver who graciously honoured the three year warranty which had elapsed about a month before the amp failed.
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