Members WRGKMC Posted September 10, 2015 Members Share Posted September 10, 2015 Boom. Your amp becomes a mess, and it also requires decontamination when being repaired. Old caps contained PCB oils a known cancer causing chemical. If the chassis isn't cleaned properly, the heat from the tubes can give off fumes, or the oils can migrate to the chassis exterior where they can come in contact with your hands. All this can be avoided with maybe $40 for caps and a soldering iron. This is the signs of caps leaking or ready to blow if they haven't shorted out yet. These have a relief valves that bubble up. An amp with caps in this condition shouldn't be plugged in. This is how it blows chunks when it shorts. Hopefully it doesn't take out the transformers and tubes as well. All that aluminum foil can short electrical contact. Never ever put a higher value cap in an amp. If the normal fuse blows, the most likely cause is a shorted cap. I'd bet someone stuck a high value fuse in this one which caused the cap to blow. Link to comment Share on other sites More sharing options...
Members Chordptrn Posted September 11, 2015 Members Share Posted September 11, 2015 Old amp stored in a closet. http://www.thegearpage.net/board/index.php?threads/tech-wants-to-replace-components-in-vintage-fender.869581/page-2http://www.thegearpage.net/board/index.php?threads/need-help-identifying-a-tweed-fender.862844/#post-10205438 Link to comment Share on other sites More sharing options...
Members WRGKMC Posted September 11, 2015 Author Members Share Posted September 11, 2015 Yup. I saw many amps with similar issues during my repair days. Rust, dirt and disintegration of parts just from aging are all problems. Anything with rubber or foam eventually liquefies into chewing gum and can become very nasty to remove. Link to comment Share on other sites More sharing options...
Members guitarcapo Posted September 11, 2015 Members Share Posted September 11, 2015 I had a filter capacitor can go bad recently on a Magnatone 480. It was a 40/30/20/20 can that had been recently serviced by a tech who simply replaced the first 40uF cap by bypassing that node and strapping a Mallory 40 uF/450V cap inside the amp...leaving the rest of the can to still work. After a few months it started making this sort of zapping sound if you turned on the standby too soon after turning the amp on. In retrospect this was arcing of the next 30uF cap in the can. Then one day smoke starts coming from the amp. I open it up and see the smoke is coming from a 10 watt resistor on the rail glowing orange.The second cap had shorted and was sending all the current through that one resistor. I replaced the resistor and the entire can and the amp was fine again. The original tech should have just bought a new can for $50 or so and done the job right the first time. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted September 11, 2015 Author Members Share Posted September 11, 2015 I noticed some breakup and loss of gain in the bass channel and I hear some slight garbled tone from AC leakage in one of the preamp tubes. So yesterday I bought a pair of F&T Dual Electrolytic caps............ to replace the "Black Whale" caps in my Blackface Bassman amp. I could have bought pairs of 25uf caps but I wanted to keep it true to the design and the F&T caps are supposed to sound the best, even if they were a bit more expensive at $13 each. It doesn't pay to go for ultra budget brands in some cases (or expensive boutique for that matter). W well know brand likely has the best tolerances, and with todays caps that's probably twice as good as they were back in the day before they had computer testing. I replaced the original power caps with Sprague Atoms which seemed to do the trick. a few years back but I hadn't done any replacements in the preamp section. I figured I'd start with The Whales then move to the blue molded ones if needed. The blue signal caps are much less likely to have issues then the electrolytes because they aren't electrolytic and see much lower voltages. I'll likely swap the preamp tubes at the same time. I don't use the amp a whole lot and the worst thing you can do to an amp is not use it enough. The electrolytic oxidation on the aluminum foil breaks down with non use and they are much more likely to break down and fail on power up. Like batteries, they need current to restore their charging capabilities. They can begin to leak if not used. Recapping doesn't mean you have to replace all caps either, just the ones that see higher voltages and can cause major problems when they short out. The rest come down to symptoms. If they cause tone or static issues like they are in my case then you seek out the ones that need replacement. If you just randomly change them all, the amp may see drastic tonal changes and may sound like a completely different amp, and not always for the better. Link to comment Share on other sites More sharing options...
Members pk1fan Posted September 12, 2015 Members Share Posted September 12, 2015 I repaired TV's back in the 70's and swinging a cap leg was something we did at times but not a preferred method of repair . You are right change the can , it is a ticking time bomb . Link to comment Share on other sites More sharing options...
Members Mr.Grumpy Posted September 14, 2015 Members Share Posted September 14, 2015 I'm in the middle of re-capping my Music Man combo. I replaced the high-voltage filter caps a few years ago, but this amp also has a bipolar +/- 16 volt power supply for the preamp, and a 22-volt output for grid bias, so there's a total of five low-voltage electrolytics for the low-voltage power supply, and they use a rather crude (by today's standard) voltage regualtion - zener diode shunt. The zener for the +22 volt supply looks like it's been cooked, so I'm going to replace that too. There's quite a few electrolytics in the signal path too, and I'm replacing those as well. Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted September 14, 2015 Share Posted September 14, 2015 Old amp stored in a closet. http://www.thegearpage.net/board/index.php?threads/tech-wants-to-replace-components-in-vintage-fender.869581/page-2 http://www.thegearpage.net/board/index.php?threads/need-help-identifying-a-tweed-fender.862844/#post-10205438 They mention the possibility of a mouse getting in there, but I don't see any signs of that. I've had the not so fun experience of seeing what happens when a rat gets stuck inside a Blues Deluxe, and the outcome wasn't good for the rat - or the amp for that matter. Still, it didn't cause any caps to blow - the rat just caused the amp to short across the tubes and took out the entire power amp section of the amplifier. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted September 14, 2015 Author Members Share Posted September 14, 2015 You find allot of strange things in amps. Mostly bugs. One time I had a kid bring me a stereo in for repair. When I got the back panel off I found a stash of weed and contraceptives in there. Shortly after he had dropped it off I got a call from the guy all in a panic asking me if I had looked inside and if I'd call the cops on him. I told him I had and hadn't seen anything except a foil wrapper from something had gotten caught in the motor gear. As you can guess the kid was beat red when he came in to get his unit. I don't think I even charged him for more then a diagnostic fee. I told him to find a better place to store things. Electronics are likely to smoke when they come in contact with illegal substances. Link to comment Share on other sites More sharing options...
Members guitarcapo Posted September 17, 2015 Members Share Posted September 17, 2015 Remember a kids's toy called "Lite Brite"? I bought an amp on Ebay that was LOADED with those little plasticpins. Apparently the owner's kid had dumped them all it through the input jack for some reason. Link to comment Share on other sites More sharing options...
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