calling jimmym!! b25 help.

[spaz21387]

So I just spotted a ampeg b25 on craigslist. The guy says its 16 ohms. Can this handle a 4 ohm cab or not?

[s_mcsleazy]

this thread was started 2 mins ago and he isnt here yet?

CALL THE POLICE, JIMMY IS MISSING

[spaz21387]

Originally Posted by s_mcsleazy

this thread was started 2 mins ago and he isnt here yet?

CALL THE POLICE, JIMMY IS MISSING

ha good one. I know how hes the tb ampeg expert in here.

[s_mcsleazy]

Originally Posted by spaz21387

ha good one. I know how hes the tb ampeg expert in here.

agreed

[hennessybass]

Originally Posted by spaz21387

So I just spotted a ampeg b25 on craigslist. The guy says its 16 ohms. Can this handle a 4 ohm cab or not?

I would say NO. It's really best to run tube amps at the recommended load. Not doing so might be alright, but it might not - you're pretty far off between 16 and 4 ohms.

[BassmanPaul]

i think you'll find it's 16Ω or 8Ω. I would not try a 4Ω load with this amp.

[spaz21387]

So where Do I find a 16 ohm cab?

[dog1]

Yup. I had a B25 a long time ago. You should run it with an 8 ohm cab

[hennessybass]

Not to spread bad info here, but....
the amp is designed to be used with one or two 16 ohm cabs. One 16 ohm cab in the "speaker" jack, and you can add another into the "ext speaker" jack. The switching OT taps make this possible while keeping matched impedances.

Or, plug an empty 1/4" plug into "speaker," and a single 8 ohm cab into the jack labeled "ext speaker 16 ohm." This will give you a matched 8 ohm impedance.

[dog1]

Originally Posted by spaz21387

So where Do I find a 16 ohm cab?

I don't know of a bass cab that is 16 ohms. Buy an 8 ohm cab

[Bulltrout]

The B25B cabinet is 16 or 4 Ohm and can be switched between the two impedances.

[hennessybass]

Originally Posted by dog1

I don't know of a bass cab that is 16 ohms. Buy an 8 ohm cab

2x15 -- 16 ohm cab from fliptops -- designed for your B25B!


Fliptops

[spaz21387]

I think I might jump on the b25 then. Its not mine yet but theres a pretty good chance it will be.

[JimmyM]

Sorry...I was out living a life...I'm back to my little box now

Those in the know say it's generally not a good idea to run higher impedance loads than your tube amp output transformer can handle, but apparently it's not such a bad thing to run at lower impedances than specified. Jess Oliver often recommended people run their B-15's at 4 ohms to eke out a little more clean performance out of them. 8 ohms is easy with a B25, though...just stick a dummy plug into the second speaker out and it opens the 8 ohm tap for the first.

[Ben B]

Originally Posted by hennessybass

Not to spread bad info here, but....
the amp is designed to be used with one or two 16 ohm cabs. One 16 ohm cab in the "speaker" jack, and you can add another into the "ext speaker" jack. The switching OT taps make this possible while keeping matched impedances.

Or, plug an empty 1/4" plug into "speaker," and a single 8 ohm cab into the jack labeled "ext speaker 16 ohm." This will give you a matched 8 ohm impedance.

You are correct about the switching tap, but it's on the extension speaker jack, not the speaker jack. So, you plug the empty plug in the extension jack and the speaker cable in the speaker jack.

Or if I'm reading the schematic correctly, you may be able to just plug the speaker cable directly into the extension jack for the 8 ohm tap--not sure about this, and I haven't tried it. Can someone check the schematic tand let me know if you agree?

OP. Another option is to run a B-25B with 2 8 ohm cabinets (as I do). You can do it ONLY IF you have a series speaker cable made. I am not sure they are commercially available, so, you may have to make one or have an amp tech make it for you if you don't feel doing electrical work.

Ben

[coreyfyfe]

There has to be something in the main output first or it shorts and you don't get any output. had the same issue with my v4 and svt when I've plugged into the wrong jack.

[spaz21387]

thanks for all the help. Ill try and go for this amp Ill be back with pictures If I can pick up this amp.

[SBrown]

I owned a B25B for a few years, I I can tell you its a beautiful sounding amp. You will hear people recommending tube swapping to increase power, or solid state rectifiers for tighter lows, but I think the best thing is to leave it stock and enjoy it for what it is- possibly one of the finest recording amps/sane volume gig amps there is. Just dont be un-reasonable about what you expect from it. It wont cut it in a very loud/no PA support rock band situation. But if you can regularly mic your cab, and play in blues or country type of situations, (or any genre where the volume is under control) you will be sittin in the mix with tone that is sublime. I had really good results using the Delta 15A speakers (JimmyM's recommendation, thanks) 8 ohm each, in a 2x15 cab. Mine was the B25B cab with the CTS drivers, I just dropped in the Deltas to preserve the stockers, and got all the good of the originals, plus better highs, tighter bass, and more volume. They still sounded very vintage. I agree 100% with the above advice on the dummy jack. Just insulate it with something, it might be shockey. I also agree that the old Ampegs can handle load mismatch better than most amps, because of their over engineered trannys. I hope you enjoy yours as much as I enjoyed mine.