Unfixable B15?

Discussion in 'Amps and Cabs [BG]' started by into the white, Feb 6, 2018.

  1. into the white

    into the white

    Feb 26, 2015
    My blue line B15 died on me a few months ago (had been playing it, put the bass down for 5 minutes, and came back to an amp that had shut off and wouldn't turn back on). It's blowing fuses now upon powerup. I finally got around to taking it to a tech, who in attempting to diagnose it found mods done to the circuit from a previous owner, and he has told me that it's essentially unfixable, because the damage that was done with the mods make it impractical to fix.

    Though I don't have an electrical engineer bone in my body, I'm no stranger to having vintage amps repaired and I'm having trouble wrapping my head around this being possible. Is there something weird about the early 70s B15N's that makes them an especially tough circuit to work with? I can't imagine that every major component failed at once, so am I naive to think that the worst case scenario here is something like de-modding it and replacing a blown transformer?
  2. beans-on-toast


    Aug 7, 2008
    You have to wonder why the tech can't provide a cost effective solution. I suspect that they are too busy to take this on.

    The PCB may be badly damaged. Even with damaged traces, a piggyback turret board over that section of the board is one way to go.

    Below is a 1973 B-15 circuit board courtsey of sjrash, Scot. It's one sided, a pretty basic board.
    If there isn’t one on the tray, here is a schematic: https://www.talkbass.com/attachments/ampeg_nf_1968_ii-pdf.830489/

    73 B-15N labels V2.jpg
    Last edited: Feb 6, 2018
    jazzbass_5 likes this.
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    When the modifications are done poorly, or not documented, many professional techs won't waste their time and your money on s repair that may be impossible to do correctly. It's just not worth the hassle, and the likelihood that it will be unreliable and come back to bite him in the ass.

    I totally understand where he is coming from. Too many unknowns, and too much time required to sort out what may have been done. To do it right likely costs more than the amp is worth.
  4. basscooker

    basscooker Commercial User

    Apr 11, 2010
    Northern KY
    Cab fan, hobbyist
    OP, sorry to hear about this.

    Is a re-build something you would consider? If all the major components are still there (orig tranny, chassis, ps, pots, sockets etc) you may be in a position to ask if he can strip it and clone a new build. This obviously will cost a bit, but you do already have the most expensive and/or hardest to source parts. This is of course assuming none of the important parts fell victim to the mod failure.

    Of course you could source an unmolested one that is DOA or a bit rough and see about him using the best of both to make one good one.

    I may also be way off with this. Although they aren't super rare, it sucks to hear about another one gone forever.

    Good luck.
    MobileHolmes likes this.
  5. blubass


    Aug 3, 2007
    Modesto Ca
    Current: Blackstar, DR strings, Nady. Previous endorsements with: GK, Rotosound, Ernie Ball, Cleartone, EMG, Dean, Dava Picks, Rebel Straps, Dickies
    In your situation, there is no, "what's the worst that can happen". You can absolutely tackle this as a project yourself so long as you have some solid electrical fundamentals, safety stuff being first and foremost.

    This is a gross generalization of the knowledge needed, but all you're doing at this point is copying the schematic with wires and components of the correct values (and hopefully quality materials).

    It is imperative that you can read the bands on a resistor, understand the values and polarity of diodes, capacitors, transistors, read schematics, etc.

    You don't have to be an engineer, but it does take a healthy dose of knowledge, time, and money.

    What's the amp worth to you?

    Keep in mind, i'm just saying things like needing knowledge. I also have some college background in electronics and several expensive books on the subject. Sometimes the correct amount of knowledge to do the repair can easily cost more than the repair itself.
  6. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    The de-modding, or at least deconvoluting the mods without a road map, will take time, and time is money. I could understand the tech being hesitant to address those issues. Outright saying it's unfixable I wouldn't agree with, but a budget busting repair bill I could certainly see.

    Replacing the transformer is pretty straightforward and the old B15Ns in general have a propensity towards wearing them out as they age with exactly the symptoms you describe here. Repro transformers pre-potted are available but cost a decent amount.
  7. timv


    Jun 7, 2000
    Chandler, AZ
    I would get the amp back, take a pic of the insides and post it here.
    Those amps aren't that complicated and I'm not really sure what could be done mod wise to make it completely irreversible.
    Unless traces were cut/jumpered.
    I'm sure it can be fixed and it may just be that tech doesn't want to work on things that take extra time.....
    BassmanPaul and Bim1959 like this.
  8. micguy


    May 17, 2011
    Normally, I would agree (I just took apart a piece of gear I recieved yesterday to do a mod a couple hours after it arrived), but there can be a point where things have gone too far. A co-worker once asked me to help him redo an old tube amp he had. I was gung ho, anticpating a good chalenge, until....I saw it. It was so hacked to bits, that, honestly, I would have feared for my own safety just working on the thing, and I couldn't in good consciense envision turning that thing back out into the world, with a human wired to it.

    Hopefully your amp isn't that far gone - I'd try another tech if I were you - a second opinion as it were.
    MobileHolmes and S-Bigbottom like this.
  9. As long as you can get parts it can be fixed.
    How much time, trouble and expense is another issue.
  10. bobcruz


    Mar 10, 2004
    I'll take that piece of junk off your hands to save you the trouble of recycling and e-wasting it...would a six-pack of your favorite brew be about right? ;)

    Seriously, sorry to hear about the problem and good luck with resolving it. Bob
    dbase likes this.
  11. seamonkey


    Aug 6, 2004
    If you like the pre-amp part, maybe just ask him to mod it to use it just as a pre-amp.
  12. dbase

    dbase Gold Supporting Member

    Jan 3, 2008
    South Jersey, USA..
    I agree with Agedhorse, but I'm thinking here that if the tech was smart enough to notice modifications, then he should be able to trouble shoot why the amp failed. and repair the problem without getting into any modifications. I mean the amp was in running condition. You just didnt find it in the trash and asked him to get it running. Give it the sniff test, maybe a resistor or capacitor must have burned out or failed that can be replaced. Unless the whole circuit board was fried or a bad transformer..either way,. I'll give you two six packs of your favorite beer for it. ;)
    Last edited: Feb 7, 2018
  13. into the white

    into the white

    Feb 26, 2015
    Thanks for all the replies all. My concerns have been eased slightly, and it sounds like a second opinion is for sure the way to go.

    It is funny - this is the second time that taking an oldie to a tech has revealed some internal changes that even the person I purchased it from had been unaware of. As I was happy with the sound until it died, I'm hopeful that dbase is on the right track and a different tech may be able to sniff out the problem even if it doesn't mean fully reverting it to stock.
    beans-on-toast likes this.
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    The challenge techs face is the possible consequences that modifications may have been involved with the failure, or that unidentified modifications may cause another or different failure in the future. There is nothing worse than putting the time into fixing an amp only to find additional issues caused by previously unidentified modifications.

    The alternative is for the tech to not warranty the repair, but IME this causes more bad will issues than just walking away from it.
  15. BadExample


    Jan 21, 2016
    And regardless of pre-repair conversations. a failed repair can and will result in negative posts on ever web forum remotely related to any sort of audio. Not saying this about the OP, but most people forget the agreement as soon as the product lets out a poof of smoke and the tech won't fix it for free.
    Munjibunga, BassmanPaul and agedhorse like this.
  16. BassmanPaul

    BassmanPaul Inactive

    Unfixable B15? There ain’t no such thing! They were designed to be easily fixable. :)
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Until some hack gets into it and makes it uneconomical to repair. Why spend $000 fixing something that you can buy used in unmolested condition for $700 (as an example).

    I see this all too often, an otherwise inexpensive, simple repair f**ked all to hell by a hack tech or hobbiest resulting in a paperweight.
    BadExample and BassmanPaul like this.
  18. BassmanPaul

    BassmanPaul Inactive

    I agree Andy but, cost aside, any B15 can be repaired even if it ends ups as a labour of love. :)
  19. wagdog


    Mar 20, 2000
    Der Waffle Haus
    It's the old adage:
    Feasible, yes. Economical, no.
  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
    Well, yeah, ANYTHING can be fixed... I could even lay out a new PCB, custom wind a transformer, fabricate a new chassis... I could even build a brand new reproduction from scratch replacing every messed up component. I think there is a not so fine line between what's reasonable and what is not.
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