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Ampeg B25 Questions

Discussion in 'Amps and Cabs [BG]' started by Fat Steve, Nov 13, 2013.

  1. Fat Steve

    Fat Steve The poodle bites, the poodle chews it.

    My band mate has an old as dirt SVT, and I can't seem to figure out what era it is or what wattage it may be. I was trying to price out some parts for it to get it back on the road. He has a matching Ampeg cab with 2- 15" speakers in it. Any ideas?

  2. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    That's a B25 or B25B.
  3. Fat Steve

    Fat Steve The poodle bites, the poodle chews it.

    Thank you sir
  4. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Saw that second pic with my glasses on this time ;) Definitely a B-25. I believe it's 55w, and kind of an oddball, in that it's designed to use two 16 ohm cabs. I imagine the cab your friend has is 16 ohms.
  5. nysbob


    Sep 14, 2003
    Cincinnati OH
    It's a nice sounding amp if you can deal with the impedance issue.

    Just for future reference, an SVT has 6 power tubes and handles on the sides, not the top.
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    A lot of rust on the chassis but that can be cleaned up. Maybe the ocean air got to it.

    As Jimmy said, the B25B is set up for one or two 16 Ω cabs. The output transformer has both 8 Ω and 16 Ω taps. With a dummy plug you can connect a single 8 ohm cab which makes life a little easier.
  7. That amount of rust really would have me concerned, how much oxidation has set into the switches, potentiometers, jacks, and sockets? Fortunately the transformers didn't look too bad.

    The speakers themselves also may be damaged.
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I was thinking the same thing about the transformers. The one in the pic looks to be in good shape. No rust on the plates.

    I restored a Fender blackface amp whose chassis was similarly covered in rust. Everything else was in pristine condition. I stripped it down to the chassis and removed the rust.
  9. Yep, I just got done restoring an old Epiphone with even worse rust. Stripped the chassis, sandblasted it, and had it re-chromed. But I replaced every pot, switch, socket, and jack on it; even made a new eyelet board (was easier than de-populating and re-populating the old eyelet board).
  10. Jens1


    Sep 6, 2013
    Help please,

    can I plug instead of a dummy plug 8 ohm cab to have 2 8 ohm cabs. I know the answer Will probably be no, but just to make sure.
    Can a transformer be modified so that I can have 2 8 ohm cabs?

    Thanks for your replies.
  11. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    You could wire a series box for the two 8 ohm cabs to present a total 16 ohm load on the primary output tap. That may come with its own host of issues but would work.
    Jens1 likes this.
  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The series box described above would run the amp at the proper impedance with the two 8 ohm speaker cabs connected. I've seen series connection boxes for sale on the internet. Each cab plugs into the box, then a cable goes from the box to the amp.

    If you plugged the two 8 ohm cabs into the amp, the amp would see 4 ohms instead of the 8 ohms that it is expecting. There would be an impedance mismatch. Some people do run these amps this way.
    Jens1 likes this.
  13. Bill Hughes

    Bill Hughes

    Oct 17, 2013
    Probably 1975. Look for component date codes. All that rust was from bad metal prep. I think we moved to Tennessee in 1977.