Help with Ampeg B12

Discussion in 'Amps and Cabs [BG]' started by valveamp101, Jul 26, 2009.

  1. valveamp101


    Jul 26, 2009
    Milwaukee, WI

    Please excuse my naivete as this is my first post and my first Ampeg. I have done some research and have found a decent amount of info but thought I'd open this up to people who can tell me much more I'm sure than what I've found.

    I recently picked up an Ampeg B-12-NC. From my research it appears it's from 1964 (according to serial #) and it's in good working order and pretty decent cosmetic condition. What does the 12 stand for? The cabinet has a 15" speaker and looks original to the cab. The schematic I found lists both the B12 & B15 as the same circuit...Is this correct? What really is the main differences of the two amps?

    I got this amp for a steal and it has found a loving home in the studio. I probably need to do a cap job and am gonna do a good cleaning soon. Are there any other components I need to be aware of maintenance-wise on this amp (other than the typical pots, etc.)? I work a lot on vintage guitar amps (although I am still learning the ropes) so I know the typical things to check. Specifically interested in knowing about the tranny's and components that may be only found in the Ampegs.

    Any advice or help in general is much appreciated!!

    Take care,
  2. BassmanPaul

    BassmanPaul Inactive

    If I have it right the B15 series came with a 15" CTS or an upgrade to an Altec 15". The B12 had a 12" speaker. The amps were virtually identical. I've heard of other cases like yours where the 12 came with a 15" so possibly there was some cross pollination either at the factory or later.

  3. G00D+~VIBES


    Nov 21, 2008
    Kansas City
    I can't help here, but if you don't get enough answers or help you should consider PMing JimmyM. Pretty much the resident old Ampeg Guru.
  4. Vintage-Blue

    Vintage-Blue Gold Supporting Member Commercial User

    Feb 13, 2008
    Cincinnati, OH
    Owner, Vintage Blue (repro cabinets)

    The 12 in B12NC refers to a 12" speaker. The B15N and B12N amps were the same amp, as can usually be seen by the fact that they share the same schematic. The only difference was whether they came with a 12" cabinet or a 15" cabinet. All of them that I've seen have been silk-screened on top of the chassis with "B15N", whether they were part of a B12 or B15 combo. Is yours labeled differently? (I'm wondering, since you refer to it as a B12, even though the speaker is a 15).

    The B12 cabinet was smaller, and there was just enough space to fit a 12" speaker between the port covers:


    A '64 B15NC would have had a 15" speaker mounted in a larger, double-baffled cabinet. There is also a good chance that it still would have had a chrome socket on the back for a tilt-back rod:


    I'd like to see a photo or two, if you have any. No matter what, it sounds like you came across a nice amp - congratulations!
  5. valveamp101


    Jul 26, 2009
    Milwaukee, WI
    Thanks everyone who posted for helping out. I presumed the 12 & 15 meant speaker sizes but wasn't positive. It sounds like the label inside the cab is incorrect then. The silk-screened label on the amp is unfortunately worn away. It does have the chrome socket on the back and it is for sure a 15" speaker.

    I can post more pics if anyone is interested; but here is a pretty lousy pic due to my now old digital camera and bad lighting skills.

    I picked this amp up along with two other vintage amps and some recording gear all for $250! This could not have happened at a better time too. I'm in the midst of working with an old school R&B band which I think this amp will work well for.

    Attached Files:

  6. markjazzbassist

    markjazzbassist Supporting Member

    Apr 19, 2005
    Shaker Heights, OH
    definately looks like a 15 from the pic. interesting.

    nice amp, enjoy her!!! i love mine :)
  7. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Mark from Vintage Blue and David (beans on toast) are the resident Portflex experts here. I know a few things, but those guys REALLY know Fliptops.

    So you can look inside the chassis tray for the schematic. You can usually see if it's still there through the slot the plexi logo goes in. I've not heard of a B-15N with a B-12N-labeled head, but I've heard a lot of the reverse happening. Doesn't mean it didn't happen at the factory, though. Ampeg had a good system back then but they tended to throw out the rulebook occasionally.

    But when you paid $250 for this and two other amps, all I can say is "Who cares if it matches or not?" :bassist: Should be fine for live work as long as your band isn't too loud onstage and you have a solid PA to mic it. I use one all the time for my oldies band.
  8. Vintage-Blue

    Vintage-Blue Gold Supporting Member Commercial User

    Feb 13, 2008
    Cincinnati, OH
    Owner, Vintage Blue (repro cabinets)
    Yep, that's a B15, with the double-baffle cabinet. $250 would be a steal for that by itself! It's too bad the power transformer has been replaced. If you ever wanted to go back to the original look, potted replacement transformers are available from a few places for around $200. It also looks like there has been something installed right next to the transformer; perhaps a large choke? I wonder what that's all about??
  9. beans-on-toast


    Aug 7, 2008
    What a great find for the price! Since you got some recording gear with the amp, maybe someone reworked the power supply to make the amp perform better for recording. The replacement power transformer looks beefier than the original (more bass). I would guess that the other smaller transformer is either, as Mark said, a choke, or perhaps a filament transformer for the heaters, or a 600 ohm output transformer. A choke has two wires, the filament transformer would have four wires.

    The first thing to do is to get the correct schematic for your model and figure out what modifications were performed. Check that the tubes are 6SL7GT's, 6L6GC's and a 5AR4. The amp might be running on something else. I would check out the power supply caps and the two electrolytics on the cathodes of the phase inverter (25uF) and 6L6GC's (50uF). Also convert the power cable to 3-prong if it hasn't been done.

    I wouldn't be too fast in undoing any changes that were made. They might be making the amp sound better.

    havnjero likes this.