Help with Ampeg B12

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.

Paul

 

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.

 

Tom,

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!

 

definately looks like a 15 from the pic. interesting.

nice amp, enjoy her!!! i love mine

 

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?" 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.

 

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??

 

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.


David