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Hi,My amp, ARC Classic 120 monoblock (year 1992), are giving me problems. The sound has deteriorated to a stage where highs become unnatural, thin and splashy; the mids also thin and lack of body. I changed to new tubes (Billington 6550C) and it does not help.
A couple of technicians had checked the amp and found nothing wrong -it is still operating well albeit with a less-than-optimal sound.
A few months ago i detected some moisture on top of one of the Philips electrolytic caps. Another strange thing is that all the plastic covers that sit on top of the electrolytic caps start dropping off due to some sort of "expansion" of the caps. Are these giveaway signs that the capacitors have reached its age???
Please advise, i am very very puzzled and troubled. ARC quoted me USD1080 on the caps (12 pieces of them) and i can't take a chance without knowing for sure that the problem lies on the caps.
Follow Ups:
I have rarely seen a large can high voltage electrolytic capacitors fail. Most I viewed are from organs or shortwave radios from the 1950s & early 1960s. Issue with this post is most organs do not have much over a few thousand hours use over that long period & radios use lower voltage in the 180 to 250 volt range. As for the smaller individual capacitors, these lose life much faster than large can type.40-50 years is way over any recommendation to keep an old high voltage cap in place. Point is I would not risk the health of an audio amplifier with an old electrolytic capacitor(s). For the average 40-60 dollars, I replace all electrolytic caps to ensure I have peak performing gear.
That $1K quote is off the wall for a cheap audiophile like myself, however find a way to replace them.
Normally, the design life of older electrolytic cap is 1000 hr at 80 degrees C and will last longer for lower operating temperature, possibly double the life with every 10 degrees lower(law of chemical reaction), There are exceptions that the cap can last more than 10 years and my actual experience with my Sony VCR(bought new around 20 years ago) so I witnessed the actual deterioration and the cap lasted around 18 years.However, it's at your own risk to operate equipment with components stressing beyond limit of design life.
Some modern caps are designed for 3000 hrs as per RS on-line publications.
It is a norm to replace the older electrolytics if in doubt and also subject to stock available at reasonable price. For this unique case, it involves the kind of money and it would be better to check the ESR readings of individual caps prior to replacement. An ESR meter from Dick Smith is a very handy equipment to check the general condition of the caps without dissembling any wires. A fairly ingeniuous device which has saved me a few hundred bucks from the date of purchase. The other piece of instrument I haven't got is a Sprague TO-6/7 capacitor tester which actually tests the cap's leakage and dissipation factor on actual cap operating voltage but you need to dissemble individual caps, which is a bit impracticable.
Just an fyi - although most people will say that technology keeps improving components, newer caps may or may not sound better in a vintage amp. ARC has historically been known for showing a keen understanding of the intersection of electronic circuits, their components, and the resulting sound. Probably more so than almost all manufacturers, they have spent a great deal of effort tweaking designs while simultaneously listening to the resulting sound. When they design an amplifier they make decisions based in part on listening sessions. Sometimes they make the decision based on analysis of the circuit, but some times/most times they let their ears guide them. When they made your amp they went through this voicing process. When you put in the latest and greatest caps you aren't going to have the benefit of the original voicing process. The new sound will likely be somewhat different - possibly better, and possibly just different. If you were happy with the original sound and want that same sound you need to find the same parts - which may or may not be avaialable today. Just an fyi. Let us know how the amp sounds with new caps vs. the old caps.
I can't speak to all the types and values used in every instrument, but I would not necessarily advocate a hard and fast time-based rule about changing out electrolytics.How conservative the designer was can play a decisive role in how long a filter cap should last. It doesn't surprise me that some of the high end instruments are seeing early failures; they are prone to be engineered less conservatively than the older classics. That's not to say that all vintage designs were conservative; there are some exceptions that are confirmed cap killers. But twelve years seems terribly short, under any standard. And almost $1,100 to replace a dozen filter caps sounds like typical high end theft to me - regardless of what designer cap brand they are.
The design of the capacitor itself is a substantial factor as well in determining its service life. In many of the vintage instruments I restore, it is typical for a 35 or 40 year old FP multisection can to reform up and operate perfectly fine at full WV. But is is also typical for most of the smaller electrolytics to be shot. You'll even get a fair share of failing small electrolytics with 20 year old gear.
But I would never advise anyone to recap something at a certain age per se without considering the instrument design and specific capacitors involved.
Don't condemn the filters because their plastic sleeves fell off; it's also possible that the sleeves themselves shrunk and broke open becuase of age and heat. Any fluid coming out of the seals of a modern electrolytic is a red flag. But "moisture" on the top of a radial cap would cause me to want to know what the fluid really was, as seepage through the top is somewhat unusual; the usual way the electrolyte gets through the top of a radial is when it explodes.
The best way to know if your capacitors are failing is to check the circuit on a scope for excessive ripple. If you hear a 60 hz hum, then you definitely have a problem. FWIW, the "power" of the power supply always comes from the power transformer; it's the job of the filters to keep up with the phase changes to hold the AC ripple under a specified threshold. If the ripple is below specification, then the filters are doing their job.
I'd find a local technician to check it out for you before you recap anything. Although it seems you have already.
hi jim, electron, jim etcthanks for the valuable input.
i called leonard of ARC just now and he too advised that i should change the e-caps after 10 years. he further told me that of late there has been a lot of older ARC power amps returned to the factory for repair/replacement due to bad e-caps. so that is really reassuring.
i can only get BHC Aerovox e-caps in my country. leonard said BHC is good cap. the only issue is the BHC is 1,000uF whereas my existing Philips is 800uF. the operating voltage is the same, 450V. i guess that's not a big problem.
ARC's price is really shocking and way out of my budget! Anyway, as jim wisely put it - i may even get a sonic improvement using newer e-caps!
Check the spec, electrically, a cap with lower ESR will perform better, but not necessarily sonically.If you shop from RS on-line or other suppliers, there are lots of choices but do watch out for sizes and mounting method.
Not unusual given the amp is 10 yrs old. Find a local technician,
anyone with electronics bench experience can handle this. You might
have to him him hunt down capacitors that are of the same mechanical
dimensions as the old ones. Brands of electrolytics that I like
are Siemens Long Life, any NOS Sprague, Nippon Chemicon.While he's in there, might as well replace the rectifier too. Often
rectifiers and capacitors die together (sympathetically). There
are excellent and cheap rectifiers out there now. HEXFREDs will
do the job.Last but not least, you could also entertain replacing power resistors that might have drifted. i.e. plate load resistors.
Hi, Leslie. The "sound" of your amplifier is determined to a large degree by the input tube. Hence, the amplifier might "check out" OK on the bench (not blowing fuses, passing waveforms without undue distortion, etc) but may suffer from deteriorated sound. Electrolytic caps age whether they are in circuit or sitting on a shelf. How they perform and age over time is related to how the circuit designer is using them. Are they being pushed hard with a working voltage near the "red line" of maximum permitted or are they being run convervatively? Is there is huge turn on surge that subjects them to overload shock everytime you turn the amp on? Electrolytics in general display lots of characteristics that make them a poor sonic choice. They are cheap compared to any alternative so they get used a lot.AR Corp has to cover expenses for upgrades and repairs. Figure at least $50 per hour ( a low estimate )tech time plus parts, which have to be inventoried for every piece ARC makes.
What are the 6550's that ARC recommends for the amp? Billington rebrands current manufacture for those types that are not available NOS.
It sounds like the caps probably should be replaced if you are detecting moisture. This is a bad indicator.
I would consider replacement of tubes other than outputs. The input tube(s) are sonically critical.
Hope this helps. Good luck on your quest.
From your description it seems quite likely that you should indeed replace the electrolytics that are "bulging" or are exuding a liquid. However, there is no way you have to spend $1080US in order to do that (12 caps), unless the amp uses Black Gates (which I doubt). The most cost effective thing to do is to determine the brand, voltage ratings and values of the bad lytics and then look to buy replacements from the various suppliers, many of whom are sponsors of the Audio Asylum. In some cases, this is an opportunity to upgrade the sound of your amp, if you should choose to improve on the quality of the lytics. Perhaps the ARC factory cost estimate includes labor as well as parts; if so, it's not so unreasonable. However, if you can do it yourself you will save a bundle. By the way also, the output tubes are not the only tubes that occasionally need to be replaced; you may want to replace your input and phase-splitter tubes also, especially if they are as old as the capacitors evidently are.
.....on how the capacitor is constructed and the duty cycle of the equipment and its misuse or use and storage. Aluminum electrolytics use a caustic chemical as an electrolyte that breaks down in about 20 years and you just have to replace them. If the capacitor is rated for 105 degrees instead of 85 degrees C then it may last longer but all aluminum electrolytics start to leak, secume, kaput. Oil capacitors do not give up the ghost nearly as bad and their electrolyte does not break down but they are HUGE. If you've got small aluminum electrolytics bypassing a cathode then by all means replace them regularly. I think most of your grunge is coming from aging tubes. Ray Hughes
Lord, ARC must be using ultra high-end caps or simply enjoying hugfe markups.
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