Ampeg B15-N Capacitor ID

Discussion in 'Amps and Cabs [BG]' started by Brennan, Sep 9, 2022.

  1. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    It’s what an experienced tech would need, layouts greatly reduce the time and errors when servicing equipment.
     
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  2. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    I can confirm that the blown resistor is normally a 22K 1W, the next one is another 22K 1W, the next one is a 1K 10W, all part of the power supply. Next in the image below is the so called death cap on the PT primary side.

    It's best to mount any power resistors a bit proud of the PCB to protect it. The 1K runs hot and ofter scorches the board.

    65 2.jpg
     
    Last edited: Sep 10, 2022
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  3. Bflat

    Bflat

    Feb 5, 2008
    thanks for catching that I meant 1 watt
     
    beans-on-toast likes this.
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Don't see clutch head screws very often in electronics!
     
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  5. Resistors can fail on their own. A shorted resistor is rare, but not that rare, perhaps 5% of failures. You might not see it often in guitar amplifiers, but that’s pretty limited. Not only vibration but heating can cause it too. Many hours of operation with a marginally resistive solder joint can do it. That’s an external source of heat, but no other component was involved. I have seen it many times. A piece of wire, a conductor, can fail on its own in the right environment. Of course in this case the most likely cause is the capacitor.
     
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  6. Canadian APII

    Canadian APII Supporting Member

    Feb 3, 2013
    Ottawa Ontario
    Yup. I'm an electronics tech.
     
  7. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    5/32” drivers for those screws.

    62C51236-317D-486A-9D2F-37ACCCDE0452.jpeg



    ED219D50-30D0-45AB-9295-D4DB0AD83053.jpeg

    I don’t know if they used them on the Batmobile. It was based on a Lincoln Futura body, some GM cars used clutch head screws in the headlight housing.
    80EEA15D-530D-4C7F-B258-9A8F3AA6C1C0.jpeg
     
    Last edited: Sep 11, 2022
  8. dbase

    dbase Gold Supporting Member

    Jan 3, 2008
    South Jersey, USA..
    That knarly wire looks like real Gem to me .. in fact is says so on the plug. Top shelf ;)
     
  9. Yes. If you have the amp and schematic in front of you.
    From way out here however, a couple of pics don't cut it, especially if the part numbers are not designated on the board or not visible. For instance, I can't read the value on that large capacitor from this far away.
    This is one of the hinderances to remote diagnostics vis a forum.
     
    Bflat likes this.
  10. All good points, and wise things to keep in mind when troubleshooting. However...
    I've never seen a resistor short. They may drift in value or burn open, but they don't fail in dead short mode like other components might.
    Resistors do not vibrate on their own, if vibration affects a resistor, that is a design flaw. Vibration can affect the circuit the resistor is in, but it does not cause the resistor to fail.
    Resistors do not generate their own heat. Heating is due to current flow through the resistor as explained by Ohm's law. Overheating is from a design error or another component failing.
    Bad solder joints happen as the result of design, manufacturing or repair issues. Likewise, for a stray piece of wire/loose conductor.
    All of these things are external to, and not the fault of, the resistor.
    Not understanding these things make diagnostics more difficult.
     
    Last edited: Sep 11, 2022
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  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Correct, the only resistor failures I have seen aside from occasional drift (which is VERY uncommon with carbon film or metal film) are a fracture of the ceramic body and a bond failure of the metal end caps (also VERY uncommon)
     
  12. Basslice

    Basslice Supporting Member

    May 11, 2008
    Western Massachusetts
    Here is my take on DIY. Nothing wrong with it. I actually find it funny when people claim that only a qualified technician should work on something. That is utter BS. I started working on amps when I had some problems with my Ampeg V4B. I am NOT a trained electrician, but I am a scientist and work around a lot of very dangerous equipment and chemicals that can kill very effectively. I have always been a DIY'er, even with million dollar equipment.

    That being said, I am trained how to research and solve problems. That type of training makes it easy for me to approach a problem and figure it out, whether that is rebuilding an car engine or fixing an amp. This means doing lots of research, asking questions and not willy-nilly futzing with anything. It also means getting the right tools for the job. It also means fully understanding hazards and anticipating problems.

    In the OP's case, it is concerning that a burnt resistor was confused with a capacitor. Not that it is a fatal flaw, but if such a person wants to do DIY they have a lot of learning to do. The last thing they should do it repair the AC cord and plug it in and see what happens.

    If a person is not prepared to learn and do it right, they should not attempt a project. However, if they are like me and curious and prepared to learn (and be prepared to probably spend more money that it would cost to get it serviced in a shop), I think pre-IC and SMT stuff is a perfectly good hobby and safe if you take precautions and pay attention.

    I am currently building a new 5E3 clone. Lots of fun.
     
  13. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Not common but resistors can short, arc over the body across to the leads, under conditions when the working voltage is far exceeded.
     
    Engle likes this.
  14. Basslice

    Basslice Supporting Member

    May 11, 2008
    Western Massachusetts
    p.s. If your gut picture is worth a thousand words....

    That amp has problems with the power supply. The 22K/1W is fried, which is tied to the main filter caps. If this were my project I would replace the
    Then check the traces and fix where needed. Replace both of the 22k/1W resistors. Also, I see some funkiness on the 270k resistor trace on channel 2 from the treble pot. Looks like the board is damaged. After checking that, I would put in a new power chord, ground it, and get rid of all the polarity switch and death cap stuf. Oh and check all the pots. Then, and only then, I would bring it up with a Variac and LB limiter and go from there. You probably are in for ~$60 for the caps and resistors (fliptops.net). Oh, I would also test the transformers for shorts before doing anything. If they are no good, then I would punt. I have never worked on a B15, but read a lot about their trannies and repotting, etc. That is where I draw the line.
     
    Last edited: Sep 11, 2022
    Engle likes this.
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    What you are saying is a big part of being qualified. This includes developing troubleshooting skills, learning how these things work, understanding work safety, and being aware of when something doesn’t look right BEFORE causing additional damage or safety hazard. This is not BS IMO and IME.

    This is a design/fabrication issue and not a resistor issue. There are standards and specifications that cover this.

    I would think that having a good idea of what goes into this, especially with the power (primary) modifications would be both helpful (necessary) to insure that the work is done safely.
     
    beans-on-toast likes this.
  16. Basslice

    Basslice Supporting Member

    May 11, 2008
    Western Massachusetts
    Don't get me wrong. I appreciate all the sage wisdom of people that do this for a living. I just don't think that a lot of this stuff is rocket science that needs an EE education or trade school or apprenticeships to figure out. Most of the amps and radios I work on are based on circuits and components that were designed 50 or more years ago. There is so much published on this that there is no magic involved. Now if I were to try to build, design or repair the guts of an iPhone, I would be out of my league.
     
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  17. Canadian APII

    Canadian APII Supporting Member

    Feb 3, 2013
    Ottawa Ontario
    Cool. I have two old Darius amps with no schematics. I have to draw my own schematics and pin out each connection to diagnose my problem.
     
    Old Garage-Bander likes this.
  18. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Unfortunately, designers don’t always follow standards. Resistors can also fail and arc internally due to manufacturing flaws and sometimes it takes a while for it to manifest itself. It’s rare. I’ve found that a black line can be due to an internal arc rather than a crack. For example.

    FB9CB514-E057-4762-8C1B-740255327AD0.jpeg




    One of the biggest design issues is standby switches in amps. You find them on the AC or DC side of the high voltage circuit, not always taking notice the specifications. Depending on how it’s implemented, arcing across internal switch contacts when the switch is opened can shorten the life of the switch. Old VOX amps are notorious for this.

    Even worse, along comes a tech and uses a replacement part that isn’t up to the requirements. The same can happen with resistors in an amp. The wrong part can lead to problems down the line. Some “techs” are lost on the concept of working voltage.
     
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Sure, they may be simple to someone with some knowledge and experience. That’s VERY different from somebody who can’t tell a resistor from a cap, who has a LOT more learning before “messing around” with this stuff.

    There's a big difference between not adequate, barely adequate and rocket scientist.
     
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    This is what happens when a component is used that does not meet the needs of the circuit. These days, this is addressed in products that are safety certified because resistors contain a rated voltage breakdown specification which depending on the application can make the component a CCL component.