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FDP Forum / Fender Amps: Vintage (before 1985) / Changing doghouse caps - why?

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picturevalve Wales. U.K.	Jul 9th, 2012 01:51 PM   Edit   Profile   Print Topic   Search Topic I have to sat I don't understand the obsession with changing these caps. Is it the extremes of temperature you boys get in the US of A ? I refurbed a silverface twin a few years back and the caps - after being re-introduced slowly to the world of the living, were ok. The amp had spent quite a few years in somebody's coalhouse - outside in the damp conditions we get here in Wales. I replaced most of the resistors with metal film - clean sound, but all the caps came up ok. Still going strong as part of a studio setup. So is it your climate over there, or is it an urban myth?
SoK66 Contributing Member **** USA We had the hit but Van got the money	Jul 9th, 2012 02:08 PM   Edit   Profile   Print Topic   Search Topic It's a prudent maintenance practice based upon the experinces of thousands of amp technicians. Somewhat like replacing old tires that still have some tread on them. You can leave them in there, just depends upon how lucky you feel and how much you're willing to risk.
Naked Clarke NJ, USA Southbound	Jul 10th, 2012 07:39 AM   Edit   Profile   Print Topic   Search Topic As is the case with most man made products, i.e. hot water heaters, washing machines, power cells, etc. some stay in service longer than others and many perform well beyond their rated life. As a consumer you may get lucky, but them again you may not. It is an urban myth that all regions of the US have similar climatic conditons.
Steve Dallman Contributing Member ***** Merrill, Wisconsin Ain't turned 60, but I got my blinker on	Jul 10th, 2012 08:54 AM   Edit   Profile   Print Topic   Search Topic Caps are two conductors separated by electrolytic material. This electrolytic insulator crystallizes but then "forms" when it is used. Crystallize-form-crystallize-form-etc. Eventually the electrolytic material dries out and won't form anymore. The material will actually last longer if used than if not. Caps on a shelf or in an amp in storage will age/deteriorate faster. When an electrolytic cap fails it will either open up (big time hum) or short (taking the fuse, transformer, and who knows what else.) As a cap ages it drifts up in value, but very sloppily, causing a loose, changing, farty low end and/or motorboating. As it drifts up in value it drifts down in power handling, hastening the time till it opens or shorts. These caps are like the belts and hoses in your car. NOS belts and hoses in an old car are not desirable and for the same reasons old caps are not a good idea. The time to change electrolytics is BEFORE they fail. It's simple preventative maintenance. The general guideline is around 15 years. Many caps will last decades longer. But around 15 years is when the failures begin. It's not the ones that stay good 30-40 years that are the problem. It's that first one that goes that does the damage.
picturevalve Wales. U.K.	Jul 10th, 2012 10:21 AM   Edit   Profile   Print Topic   Search Topic That would be good advice except for the fact that there is so much crap coming out of China these days that the old caps are probably better made, and then you have the counterfeits to contend with. Who can guarantee their caps these days? Are there any guaranteed manufacturers? Grateful for any pointers.
mullardgz34 USA	Jul 10th, 2012 11:34 AM   Edit   Profile   Print Topic   Search Topic Weather forecast for the US of A is: Humid with a chance of electrolytic failure
Hammond101 Contributing Member * So. Cal. USA	Jul 10th, 2012 12:46 PM   Edit   Profile   Print Topic   Search Topic Just a comment based on an amp I personally own. A '67 Pro Reverb. I bought it bone stock original in the mid '80s. I played it that way with the exception of changing some grid resistors, tubes & rebias until early 2011. A little over a year ago I replaced every electrolytic cap in the amp. 43 years was long enough. The improvement in power, clarity and punch was amazing. I did not consider the amp to sound bad nor did it hum or become farty. The only thing I noticed was a slight loss of clean headroom. The amp was gigged heavily from the time I bought it through 2005 or so. They degrade so slowly you can't really hear the difference until you do the work. The amp was kind of an experiment for me to see how long it would go. It became too valuable not to perform basic maintenence on. The loss of a PT would have hurt it's value substantially. As Steve says above, some are lucky, some are not. As a rule I put new electrolytics in anything vintage I gig with. This was exceptional service from this one. I was certainly overdue. The quality of caps today is questionable for sure. I have had issues with Sprague caps brand new out of the bag. (now Chinese made I understand) I think however when tested prior to installation they are no less reliable than caps made years ago.
picturevalve Wales. U.K.	Jul 10th, 2012 01:18 PM   Edit   Profile   Print Topic   Search Topic Ok. Thanks for the insight, not to mention the weather forecast. :)
SteavisSmokin Netherlands	Jul 11th, 2012 01:35 AM   Edit   Profile   Print Topic   Search Topic F&T caps are good quality (made in germany) caps. I never had a single problem with those.
SoK66 Contributing Member **** USA We had the hit but Van got the money	Jul 11th, 2012 09:17 PM   Edit   Profile   Print Topic   Search Topic I've stopped using the Sprague Atoms for filter caps now that the F&Ts are around. Easier to work with, 100% sucess rate for me.
picturevalve Wales. U.K.	Jul 12th, 2012 01:37 AM   Edit   Profile   Print Topic   Search Topic Interesting info. about F&T. Thanks.
SoK66 Contributing Member **** USA We had the hit but Van got the money	Jul 12th, 2012 06:58 AM   Edit   Profile   Print Topic   Search Topic They're also sold under the Tube Amp Doctor brand (TAD). Same-same.
Beatlefreek Canada Living is easy with eyes closed	Jul 12th, 2012 07:41 AM   Edit   Profile   Print Topic   Search Topic "The loss of a PT would have hurt it's value substantially. " What's a "PT"?
willie Contributing Member **** Walton County, GA. Half a century of guitar and amp service	Jul 12th, 2012 09:23 AM   Edit   Profile   Print Topic   Search Topic PT = Power Transformer. W
brawler USA	Jul 12th, 2012 01:25 PM   Edit   Profile   Print Topic   Search Topic First off, vintage caps that are damaged, leaking, or out of tolerance should be replaced. No question, these parts have already failed to a degree. New caps are required to prevent a more serious problem. Do not hesitate to replace them. But do keep the old parts, having them when you go to sell a vintage amp increases it's value to a collector. As they say on Mythbusters "Failure is ALWAYS an option". THE FAILURE RATE FOR NEW CAPS IS NOT ZERO. New caps can and do fail and the results of that failure to your amp are the same as for old caps that fail. So... are new caps less likely to fail less often than old caps? Maybe... failure rates are a whole study unto themselves. I think that as caps pass the 10 year mark the rate of failure rate of those parts exceeds that of a new parts. I have no proof of that, it's just a bit of wisdom that seems to be accepted (I'd love to see a study that shows this is true or false). Does that mean your vintage caps will fail soon? NO! There are many factors that making a generalized statement like "they are old, you have replace 'em!" inaccurate at best. Each amp needs to be looked at and evaluated to make a determination. Caps do not have to fail just because they are old. Here is why new caps may NOT be better than your old working, in spec, ones. Caps today are couterfeited. As counterfeits they are inferior parts that are quite likely to fail. This is a growing problem. Don't think that just because the part is only a few cents that it is not a counterfeit. A few pennies over millions of devices is a lot of money. There a known cases of major electronic manufacturers getting these bogus parts and it costing them millions in warranty work for product failures. The parts are many times rebranded to look like top of the line quality parts, that is where the most money is made in counterfeiting electronic parts. Beware! Many of the overseas (China, Taiwan, etc) caps are built to extremely poor standards using inferior materials. They are then shipped in hot containers to your location. Early failure is the norm. If you feel you MUST replace the caps in your vintage amp then do so only with top of the line "verified" branded caps. Only buy name brand caps from reputable dealers. Most new electronic devices fail with the first few months of being put into service (even with quality parts). If they survive that period the devices are very likely to last a long time. They can fail at anytime but statistically they quite unlikely to fail after the initial burn in period. New caps fail at a higher rate than broken in parts (up to a point then failure rates rise again but that is usually after years of service). If the caps in your amp are working and in spec, they may be the best left alone. Keeping your amp properly maintained is a good idea. New caps, especially cheap ones do not give me any more of a security blanket feeling than old caps. It is sad that this is how it is, but it's just a fact of modern electronics. I am not advocating you keep the old caps or that you replace them. Just be aware that new parts fail too and that replacing the caps out of hand is not always a guarantee that someting bad won't happen. You and your amp tech should talk about your specific amp before deciding what to do. There is no single right answer for all amps. I know my opinion on this subject does differ from some of the people here. We have discussed it before. I also know the risks of keeping old caps in my valuable vintage amplifiers. I am not foolish, and I do not keep old parts in my amps when then are better replaced with new ones. But, I also refuse to replace a vintage part that does not need it. I evaluate each part for each amp, and how that amp get played, and then decide what is best for that amp. (This message was last edited by brawler at 02:04 PM, Jul 12th, 2012)
Stratopastor Stockton-on-Tees Jivin' with cosmik debris since 1955!	Jul 13th, 2012 08:27 AM   Edit   Profile   Print Topic   Search Topic Brawler, on that basis, how often would you advise going in there and measuring the electrolytics for capacitance and esr?
willie Contributing Member **** Walton County, GA. Half a century of guitar and amp service	Jul 13th, 2012 01:28 PM   Edit   Profile   Print Topic   Search Topic In 50 years of electronics servicing, I would estimate the number of known electrolytic cap failures from new stock installs at less than 20 or so....and that's based one hell of lot of cap installs. Just stating my experience..YMMV. willie musicmenders.com
picturevalve Wales. U.K.	Jul 13th, 2012 01:56 PM   Edit   Profile   Print Topic   Search Topic Current issue of EPE has first part of a project for rejuvenating/testing electrolytics. http://www.epemag3.com/
brawler USA	Jul 13th, 2012 02:03 PM   Edit   Profile   Print Topic   Search Topic I wanted my previous post to make two points, but it was a little wordy. 1. New parts are not a gurantee against failure, they can be bad right from the get-go. Parts today are very suspect in quality and even origin. 2. Swapping out caps just because they are old is not required. It depends on the amp and the answer to the questions below, and possibly other factors. You should consult an expert for an in-hand opinion and not do anything based entirely on my opinion or anybody elses that you don't have absolute faith in. This is the internet and you need to beware. A good amp tech is worth his weight in gold. Some even specialize in specific brands and have worked on so many of them they know where the problems are for those amps. Those are the kind of people that will take the time to look at your amp and do what is best for the amp. Most of all they should take the time to ask questions and be willing to do listen to what you want. It's your amp. Ask yourself... Is the amp working properly now? Is there any physical signs of damage to the caps? How often is the amp played? Is the wall power at a voltage the amp was made for? It is taken on the road or moved around a lot? It is subject to large temp swings or humidity issues? Have the caps been checked before? Are they operating properly? Is the amp close original and worth preserving as close to that state as possible? Does it sound good? Was it abused in the past? Are the transformers original or replaced? OK, now I will answer your question directly. Here is what "I" would do. I know you said the amp was in a studio but had lived a hard life. It has been subject to heat, cold and water in storage. It already has replaced resistors due to poor storage. I would guess that it had a long time of not being played at all. In the case of your amp, it has already been changed substancially. Much of it's originality is already gone. Those are the factors I considered. I think new filter caps are probably a reasonable thing to do. Unless you know what you are doing get a good tech to do that using good parts from a reputable source. Amps carry very high voltages even when no longer plugged in and can kill you if you do not take the proper safety precautions. Good luck.
brawler USA	Jul 13th, 2012 02:18 PM   Edit   Profile   Print Topic   Search Topic > (This message was last edited by brawler at 02:20 PM, Jul 13th, 2012)

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FDP Forum / Fender Amps: Vintage (before 1985) / Changing doghouse caps - why?

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