1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Ampeg b25b cab question

Discussion in 'Amps and Cabs [BG]' started by tenbergia, Feb 15, 2013.

  1. tenbergia


    Feb 15, 2013
    Hey there,

    I have an old 2x15 ampeg b25b cab. Pretty sure they're 16ohms mono, mines been rewired to do 4 ohms by the guy that owned it before me. Im about to acquire a head that will only do 8 ohms. I'm pretty bad at this tech stuff, do I have any cheap easy options? Or will I have to attempt to rewire it back to 16ohms or pay a tech to do it for me and run my head underpowered at 16 ohms.
  2. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Find a couple 4 ohm 15"s and rewire it to series...that's about your only option other than to run it at 16 ohms. But it may work out since the B-25B is more of a medium duty cab. How many watts will the head do at 8 and 16 ohms?
  3. tenbergia


    Feb 15, 2013
    I'm pretty sure its 50 watts at 8 ohm, I'm actually going to be running a Traynor YBA-1, I primarily play guitar and while it is a bass cab I still plan on using it.
  4. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    With what you have, the options are 4 or 16 ohms only. You can swap out the spkrs for an 8 ohm cab, but I'd just go 16 ohms and call it a day.
  5. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Isn't the Traynor a tuber? From what everyone tells me, operating with a 4 ohm cab is safer for an 8 ohm tube head than operating at 16.
  6. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    The YBA-1 only operates at 8ohms?
  7. anderbass


    Dec 20, 2005
    Phoenix. Az.
    Someone could have replaced/reconed the speakers in that cab, so I'd sugest you start by using an ohm meter to confirm what ohm each of your speakers are. Who knows, maybe the seller was mistaken and it actually has a pair of 4 ohm speakers now...
  8. Unlike SS heads, it is not advised to run tube amps at a higher load so 16 ohms would not be a good option. Are you sure the amp doesn't do 4 ohms?
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Just to be sure, check your amp because the YBA had more than one revision. The YBA-1 is 8 ohms, the YBA-1A is 4 ohms.

    As was said, with some tube amps you can run them at a lower impedance and get away with it but a higher impedance is not good. So, if you have an 8 ohm amp you might be able to run it with a 4 ohm cab but not a 16 ohm cab. It would be best to ask the technical folks at Traynor what they recommend because with some amps you can get away with running a mismatched impedance, others you can't. It depends on the specs of the output transformer that they use.
  10. BogeyBass


    Sep 14, 2010
    To get 8ohms you need 2 16ohm drivers in parallel
    or 2 4ohm drivers in series.
    Only way to do it.

    With a tube amp it is recommend when running series speakers that it is series/parallel so if one speaker blows you still have another parallel load. this is impossible to do unless you have 4 drivers or 2 series cabinets. which you dont... so

    Just dont blow the speakers because running series loads is not recommended for tube amps, since if one speaker blows there is no load, and would of course present a no load situation to the amp.

    so i would find a pair of 16ohm speakers to run the proper load for the traynor.

    or just find a better amp with more taps so you can run a 4ohm load which is very common for a 2x15.

    confirming your speaker impedance and transformer impedance is a good idea to. maybe your already ok
  11. tenbergia


    Feb 15, 2013
    Yea its definitely a YBA-1 not 1A and its 8 ohms mono only (no switcher). And yes it's a tube, I've heard that its ok to run them at 4 ohms but I'm skeptical about blowing up my head. Maybe someone has some insight on this? I have another cab thats on the cheap side. Unfortunately this one is 4-16 ohms mono or 8ohm stereo each side so I don't think my other cab will help me out here either.
  12. ko stradivarius

    ko stradivarius

    Aug 14, 2006
    St. Louis
    FWIW, My 1970 YBA-1A is 8 ohm only.
    I used to run it through my 4 ohm Genz cab sometimes.
  13. tenbergia


    Feb 15, 2013
    Honestly ill probably just run it through at 4 ohms and cross my fingers, I've read that it can take it but since its older ill just have to cross my fingers. I can always try and trade for an 8 ohms can eventually. I could also temporarily run it out of my stereo cab which is 8 ohms each side. Only one side will play right? Other than that it shouldn't cause harm though? Or do you guys think I'm wrong there?