ampeg b25 questions

[bass7858]

I recently aquired a schroeder 1212L and really like it!!
So when a church i used to play for called today and offered to give me a "free" ampeg tube head i was thinkin SWEET!!
Might sound good with my Schroeder. i remembered the amp sat in a closet when i played for them but didnt really know much about it (model etc) I knew it was old as it had been in the churches possesion since it was bought new by a now deceased member in 1969.
i was hoping it was a v4(b). No such luck. B-25. Thought i remember reading on some forums where some guys liked them. So i was gonna plug into the Schroeder which is wired @ 8 ohms and see if the 2 liked each other
BUT!! Before playing and after reading some info online it appears that it was designed to use BOTH speaker jacks to make an 8 ohm load.
Evidently there were factory 16 ohm cabs.....and for the head to operate at 8 ohms both speaker jacks had to be used.
So i'm now wondering several things and hoping some of u masters may be able to enlighten me....as i dont want to hurt the head or my speakers.
1) would it be ok to just plug my 8ohm in and go for it?
2) if not...would it be possible for a tech to re-wire where it would operate comfortably with a single 8 ohm load?
3) Are any of you gurus aware of any mods that can be made to this amp to....mmm...pump it up more? i.e diferent transformers/tubes
4) would anyone know a tech to perform said mods?
as a side note...the church i got ifrom got new bassist about a yr ago and he tried to make it work....but got some distortion at louder levels. After reading what i did today and the bassist telling me what cabs he tried it thru i'm pretty sure theohmage mismatch or over load thing may have been at work. He did however take it to a local tech who re-tubed and recapped it. Pretty sure said tech would not have been savy enough to tell him about the speaker jack/ohmage thing though
Thanks in advance if you can shed any light

 

[bass7858]

Bump-ola

 

[Jazzman]

You will have to rewire the output jacks. It should take any tech 10 minutes to do.

BTW, I think the B-25B is one of the best sounding Ampeg heads of that era. Absolutely killer tone.

 

[RickenBoogie]

Those B25's are weird about the 16 ohm thing, but the tone is sublime. Have it re-wired for 8 ohns, and try it through a 15" cab for best results. Great head, btw, you're lucky to get one for free.

 

[lazyone2]

The B25 is 55 watt amp. The distortion probably happen because it ran out of head room. On my B25 max volume is at about 11:00. Thats the sweet spot where it sounds best. After that it will start to distort more and more. You have a classic great sounding amp. Please do not do mods to increase power it would also change the sound and ruin its value. It is not an overly loud amp. But it is a great sounding amp.

 

[bass7858]

Thanks guys!!! glad i didnt just plug it up and fly!!

 

[Oren Hudson]

Provided the head has not been modified, the B25B does 16 or 8 ohms - this is straight out of the owner's manuel. The B25B cab, again, if not modified, has a switch to go 4 or 16 ohms.

 

[johnk_10]

looking at this schematic of a B-25 : Invalid Link Removed
if this schematic is correct, it appears that all you'd have to do is plug an 8 ohm cab into the ext. speaker jack to access the 8 ohm tap on the output transformer and not use the hardwired xlr speaker output on the back of the head.

 

[bass7858]

no hardwired xlr on back.
1-1/4 inch plug labeled speaker
1-1/4 inch plug labeled ext. speaker
guess at some point someone may have modified and removed hardwire and installed 1/4 in plug?

 

[johnk_10]

in that case, i would have to see the inside of the amp to determine how it is currently wired. most likely, they wired it as if it still had the xlr cable but just wired it to a non-switching 1/4" jack, in which case, using the ext. jack (switching jack) would supply the 8 ohm output tap.

 

[Oren Hudson]

Appears to be original. I have 2 of these heads. Both have what you listed and there is another jack for an extension amp and a hum balance adjustment spot. Note that each speaker jack is listed for 16 ohms.

 

[bass7858]

Guys...thanks SO MUCH for your help and patience. I went and looked at the schematic....but as i have NO electrical knowledge (other than dont mess with it if u dont know about it) is it safe for me to plug in my 8 ohm schroeder and go for a spin?
Guess i could just ease into it. Obviously the guy who tried it b4 mismatched it.
thumbs up or thumbs down? safe to plug into external speaker jack or just take and get it re-wired where either jack is 8 ohms?
once again....thanks for your patience and knowledge

 

[johnk_10]

IMO it would be completely safe to plug it into the ext. jack, turn the amp on, let it warm up, take it off standby and briefly listen first to your cab with nothing plugged into it to make sure that it is working. you should hear a slight hiss or hum at idle (meaning that output is going to the speakers). if you don't then the main speaker jack is of the switched type like on a fender amp and you should turn it off asap and have the main output rewired using the 8 ohm tap.

 

[Oren Hudson]

You should be OK, since the head will do 8 ohms. But - also follow johnk_10's advice. Better to be safe than sorry. Based upon my experimenting, I don't think that it matters which speaker jack that you use.

 

[bass7858]

Okie Dokie!! Put the b25 thru her paces tonite.
First, followed everybodies kind suggestions.
1) connected 8 ohm schroeder to ext spkr jack
2) turned on, let warm up for 5 min
3) let it off stanby, was rewarded with a nice "thunk"
4) rolled ch1 volume up and down. yep..gotta slight hum
5) plugged in jazz bass into normal ch 1 and held forth
volume worked all the way up to maybe 3-4 o'clock...fairly loud ( not head splitting) no distortion. KILLER TONE!!!
plugged into bright ch1 and its noticeably a brighter sound.

Turned down channel 1 and plugged bass into ch 2.
did not work at 1st...wiggle guitar chord...got about half signal and quite a bit of hum. ok ch2 is toast. will get looked into.

then, out of curiousity...i plugged cab into regular spkr jack.
picked up about 33-40 % more volume!!!
You guys that have commented this thread now about the funky ohmage thing, i.e. speaker plug is 16 ohms...plug into external 8 ohms....
OK....all i can say is got almost 2x's more volume out of the speaker jack. which makes me wonder.............

I did buy the schroeder used. previous owner did say he upgraded the speaks with 2/16 ohm 12's. wired so it would be 8 ohms. .....makes me wonder if he wired the speaks right?

I intend to take head and cab to a tech and let him sort it out. but for right now....i got a gig on the 23rd....and this lil dude is plenty loud enuff for that 5 piece band!!

 

[lobey]

Plug a patch cable into the "high" input on channel 1 and the "normal" input of channel 2. Then plug your bass into the "normal" of channel 1.

Experiment and enjoy!!!

 

[bass7858]

ok....i dont know much about these older heads (obviously)
but what would patching it like the do or accomplish...just curious,,,too late to experimant now

 

[Oren Hudson]

Glad that you got a YEE-HAW out of it. These do have a great tone. A couple of suggestions and comments. A couple of weeks ago I began getting my two B25Bs "into shape" and discovered that channel 2 was not working on one them. I sprayed the jacks and controls with Radio Shack tuner and lubricant. That helped a lot. Try that and make sure to turn the knobs a bunch. After that, channel 2 began working. You might want to try the daisy chaining between the 2 channels. I haven't done it yet, but I've been told it provides some added options to sound and perception. Just take a guitar cord and run it from a jack from channel 1 to a jack for channel 2.

I just saw where "lobey" posted the daisy chaining idea to you before I go this posted. Since I haven't done it yet, I can't tell you much, but I've read some posts on here somewhere praising the result. Maybe do a search under B25B and it'll pop up.

 

[bass7858]

thanks for the tip!! both of ya's!!
i'm gonna take this dude to my tech buddie. he's been workin on amps for 35 yrs. mostly ss but he DOES love diddlin with tubers.
i'm gonna ask him what we can do to get "more" of what it has now without changing the tone. may be nothing more than going thru it and giving it a good cleaning. tubes were replaced in the last year....
thats interesting about patching the 2 channels...i suppose u would manipulate volume and tone on both channels?
Any personal settings/tweaks/experience?

 

[lobey]

Both channels controls work at the same time. Pretty neat if you mess with it. Two volumes, two basses, and two trebles. Had some cool tones. Definitely try it out if you get the chance.