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question about ohms with Ampeg b25b...

Discussion in 'Amps and Cabs [BG]' started by twotonetommy4, Nov 18, 2012.

  1. twotonetommy4


    Jul 25, 2012
    Hey guys,

    So i realize there is most likely multiple forums explaining what I am trying to figure out...but I was hoping someone could help since I truly know nothing about ohm ratings and what head is good to match with what cab.

    I've recently purchased a 1969 Ampeg b25b head off a guy from Craigslist, and have now noticed the head says "16 ohms" near the speaker output. The cabinet I own is the Ampeg 4x10 HLF classic.

    My question is, will this combo work? i have yet to try it out because I a do not want to mess anything up in the head or speakers. If the combo won't work, what do I need to do to make it work?

    Thanks for any and all help. Hopefully there is someone out there willing to teach me a lesson about ohms and compatibility between amps and cabinets...Shed some light on this poor soul!

    Thanks guys....
  2. RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    That amp requires a 16 ohm cab - just like it says. The cab you have is 4 ohms but could be rewired to 16 if you don't need the horn. You can also "fool" the amp into driving an 8 ohm cab by plugging a dummy plug (no cable connected) into the second output jack. What are you planning to do with it? It really doesn't have enough power to play with a rock band.

    I have one of the 2x15 B25 cabs but haven't found a head for it yet - I'd only use it at home anyways. My cab has been rewired to 4 ohms but could be wired back to 16 if I ever have need. Sounds great with the '67 Bassman I have :D .
  3. One Drop

    One Drop

    Oct 10, 2004
    Swiss Alps
    Also check the sticky here at the top if the page. All you need to know and more.
  4. twotonetommy4


    Jul 25, 2012
    Roadkill...so by dummy jacking to make it think it is running 8 ohms will be okay for my 4 ohm cabinet?

    And I've lots of reviews with people saying the b25b is their main gigging amp, plenty loud enough for all smaller-midsize gigs and rehearsals, which is I all intend on using it for.

    thanks for your help sir!
  5. RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    No - but since 16 ohm bass cabs are extremely uncommon you could then run an 8 ohm one. As I said you could rewire your 4 ohm 4x10 to 16 ohms but you'd have to know what you're doing - not something someone can explain over the web :( .
  6. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    +1 the 4 ohm cab can be re-wired to 16 ohms, which would then be a perfect match for the amp. Tube amps should always be run with a load that matches the ouput. Some amps have a swithable ouitput for 2, 4, 8 ohms, etc. Yours will do 16, or 8. You have a 4 ohm cab, so rer-wire for 16 ohms and you're good to go. Do not run it as is @ 4 ohms.
  7. twotonetommy4


    Jul 25, 2012
    thanks Rickenboogie...I guess my next question is...how do I rewire to 16 ohms, and will doing this compromise volume levels? Guess I could take it into the music shop, but trying to save $$$ if I can.