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Identifying speakers in an Ampeg cab

Discussion in 'Amps and Cabs [BG]' started by natrab, Mar 5, 2004.


  1. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Well, here's a little game for you smarties out there. I have this old Ampeg cab I got at a garage sale for $40. I'm not sure when it was made, what kind of speakers are in it, or how many watts it can handle. Here's some clues:

    Both 15" speakers appear to be labeled as such (though my eyes may deceive me):

    58054-1-8OHMS
    67-7536

    You can look for yourself on this picture:

    [​IMG]

    So It appears to be a 4 Ohm cab. That's what I've got so far. Here's a picture of the cab:


    [​IMG]

    And the back of the speaker:

    [​IMG]

    I have more pictures available here

    I'm really interested in knowing what kind of speakers these are. I PMed somed pics to AmpegInsider a while ago and he didn't think they were stock speakers. The jack plate on the back is interesting as it's selectable between 4 Ohms and 16 Ohms (though it's riveted in so I'd rather not pry it off to look at the crossover).

    Kudos to anyone who knows :)
     
  2. Eminence (67)
     
  3. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Any idea how many watts? I think this cab was only made to go with a 50 watt tube amp, but then again the speakers were replaced.
     
  4. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    Ok-Here's the deal- That is the cab for the B-25b head. That cabinet's speakers are run in series, giving it a 16-ohm impedance. The B-25B head is an only 16 ohm head. I'm sure the power rating is somewhere in the 25w/15". The head is at a local shop of mine for $275. I would buy it, but it'll only run @ 16ohms.
     
  5. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    And how do you know that the speakers aren't original?
     
  6. notanaggie

    notanaggie Guest

    Sep 30, 2003
    They are Eminence, made in 1975 in week 36 of that year.

    That puts the earliest date those could have been put into a cabinet at say a week or two after that, including shipping time. Middle of September or so if I added right.

    If that is OK date-wise for the B-25 it could be original.
     
  7. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    The only reason I thought they weren't the original speakers was because of my PM to AmpegInsider. However he didn't see the pics of the insides. He just thought they didn't look like the stock speakers. I now think they probably are original.

    So they're 16Ohms wired in series. Now on the rear plate there's a button to push to switch it to 4 ohms. Does that mean it will switch it to parallel?

    The way the wiring is done I don't see how that can work. I may pull out some of the foam to see the crossover and wiring.

    [​IMG]
     
  8. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Bah, after closer inspection, it looks like that panel was moved, and the "speaker impedance selector" switch seems to be gone. They are wired in series to looks like it's a 16 Ohm cab permanently.
     
  9. Where's the button?

    Here is what happened to your cab. The name-plate that's pictured in your post began its life not with a 1/4" speaker jack but with a black, plastic two-position impedence selection switch AND was located a few inches higher on the back of the cab. That former original location can be seen in one of your other pics and the hole has been covered with a makeshift "cover".

    So what originally was under where the jackplate is now? A 4-pin XLR speaker jack.

    Chances are the speakers are original. I would restore it to the way it was originally and have a bitchin' 4 ohm cab.

    The Original Ampeg Co. designed that cab with the selector switch to make it more versatile. By versatile I mean so that it could be used in different combinations with other Ampeg heads (Vintage) besides the B25B. For instance, in 4 ohm mode it could work with the SVT and V4B among others, etc.

     
  10. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Ahh, makes a lot of sense.

    Ok, so to make this into a 4 Ohm cab all I have to do is desolder the white cable from the top speaker:

    [​IMG]

    and solder it directly to the 1/4 jack in parallel with the bottom speaker (brown wire).

    Am I correct?
     
  11. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    So the white wires go to the other speaker? And the brown wires directly to the jack? If so, it looks like they are already in parrallel. Try a reading with a multimeter at the jack.
     
  12. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Well the white wires do go to the other speaker, which would mean the other speaker gets it's power after the first speaker. I'm pretty sure that's the definition of series.

    By soldering both speakers to the jack then they each will get a fraction of the power from the line in and the load should be down to 4Ohms.
     
  13. To wire them in parallel you need to have the negative wire from the speaker jack going to the negative terminal on the first speaker. Then from that negative terminal you need a jumper to the negative terminal on speaker #2. At that point you are done with the negatives.

    The positive from the speaker jack needs to go to the positive terminal on the first speaker and from there a jumper to the positive terminal on speaker #2. At that point you are set to go.
     
  14. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    KingOfAmps has it right. You can think of parrallel as parrallel lines in all the wires. All the pluses hooked up and all the negatives.

    In series, no connection has more than one wire. So the plus from the jack goes to the plus of speaker A. The negative of speaker A goes to the plus of speaker B. The negative of speaker B goes to the negative of the jack.

    I am pretty sure that the speakers are already in parrallel.
     
  15. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    Oh, well that means it's already wired in parallel. Right now the brown wire is going from the positive and negative terminals of the jack to the positive and negative terminals of the first speaker. Then the first speaker has a wire going from its positive and negative terminals to those of the second speaker.

    So that makes it wired in parallel I think, which is nice because I already put the whole cab back together.

    I assume that since someone did a minor surgury on this amp and took out the original jack-plate that they would have left it at 4Ohms rather than 16.

    Anyways, one last question for y'all.

    Any clue as to the kind of wattage this cab can handle? I'm gonna hook it up to my M-2000 and I don't want to hurt it if it can't handle it.
     
  16. I think you should throw on the brakes and get a multimeter before risking such a nice amp. Please don't take this harshly but your replies and pics don't sound/look to good.

    Perhaps an optical illusion but in your pic labelled "topspeaker2" it looks like the positive and negative terminals are connected??
    [​IMG]
     
  17. natrab

    natrab

    Dec 9, 2003
    Bay Area, CA
    No, they are not connected.

    There is one set of pos/neg wires going from the jack to the first speaker's terminals. Then there's another set going from the first speaker's terminals to the seconds'.

    [​IMG]

    In this picture you can see, the brown wires go to the jack and the white wires go to the speaker. I am now 100% sure that these are wired in parallel (I had a tad of confusion about that earlier on, but it's settled now).

    I tried the cab out with my amp, and it sounded pretty decent. It couldn't take too much power and didn't get very loud, however it's still a nice piece.

    I could replace the speakers with more powerful ones, but I don't think I want to mess with the cab too much. I already have good cabs for my high-power needs.

    I'm probably going to end up getting rid of this thing as I don't have too much space right now and it takes up a chunk. Maybe there's someone out there with a matching head who's been looking for this :p
     
  18. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    As pointed out, the speakers were made in 1975 according to the date code.

    The B25B came out in 1969 and was then canned about 1971, so speakers from 1975 are clearly not the original ones. They could be the original TYPE, that I can't be sure about.

    The missing switch would have switched them from series to parallel. Series wouldn't be that useful (at 16 ohms) with most current amps, but would be OK as part of a 2 cabinet setup with a tube amp having an 8 ohm tap.

    The B25B was only about 55 watts.
     
  19. Dig a little deeper and you will discover that perhaps the B25 came out in '69 and got canned in '71 but that the B25B lived on past '71 til about '76.

    I have catalogs dating to '74 and '76 that depict the B25B.
     
  20. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Hmmm. Ok, there is another place where the records aren't so good.

    So the dates are possible.