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NAD - Ampeg B25B

banikek

banikek

Sep 14, 2010
538
592
Sydney, Australia
#1
Many years ago I picked up an old, beat up Ampeg B-18 speaker cabinet. Almost all the tolex was gone and no amp was included. Since then it has gone thru a few incarnations and currently is loaded with a nice JBL 18. Today I picked up an Ampeg B25B head. Very clean. Paired up nicely with the old (now new) B-18 cab.

IMG_0921.jpg

IMG_0922.jpg


Did the plug trick on the back to fool it into 8 ohm mode. Also played around with crossing the channels etc. Sounded best with my old P bass with flats and also with an old Mosrite bass I have. Please let me know if anyone out there has some tricks or tips for me in regards to this amp. Should be fun!

Also, anyone ever use a B-18 with an upright bass? If so do you mic it or use a pickup?

thanks,
chris
 
#2
nice rig! crazy retolex job on that b-18 cab! never ran upright with a b-18 but i do it all the time with my b-15. i use a pickup...the clef revolution solo 2. fantastic pickup! i see no reason upright wouldn't kill with that rig.
 
#3
The tolex was done buy a guy here in Minneapolis who does work for Savage. I was gonna do the whole blue diamond thing but when he matched up some Fender tan tolex, Marshall grill cloth, and piping, he caught me at a weak moment. Plus at the time it was super hard to find the blue diamond stuff.

chris
 
#4
Congrats on picking up really cool amp, looks great! Is that an 8 ohm speaker? If so just use the ext. spkr. jack and you'll be fine, (I've driven 4 ohm cabs on occasion and no issues yet). You asked for tips? here's a couple.... Channel 2 has a deeper bass tone, so I plug in to "2 normal" and run my short loop cord from "2 bright" over to "1 normal". Another idea, if you have an A-B-Y box, is to run a clean signal to ch2 and an effects signal to ch1.
A very simple mod you can do is to pull the rectifier tube (5AR4), and replace it with a solid state unit. There is quite a difference, the tube slows the attack and the ss increases attack, gives the amp more punch. Some will prefer the tube, I like the ss. You can find solid state rectifiers at many tube supplies for about $10.

Here's how I do the "loop"

Picturesnov2010018.jpg
 
#5
I've been playing a Baby Bass through my B15. I run the stock diaphram pickup into channel two and run a Schaller magnetic pickup into Channel 1. Your B25 head with the B18 cab should make for a great pairing - have fun with it!
 
#7
Vistacruiser - great minds think alike! My playing around last night landed me plugging into Normal 2 for the best tone.

Another question - when you plug an 8 ohm speaker into the "Ext. Speaker" output, are you also putting a "dummy" jack into the "Speaker"? That is what I was doing.

I will check out the ss rectifier. I also tried the VT Bass pedal with it and that sounded damn good too. Not sure if that was sacrilege tho!!

thanks again,
chris
 
#8
not sacrilege at all. i always use a vt deluxe with my tube ampegs. for one thing, doubling on upright requires a 2-channel device with an eq for at least one channel. for another, i've become an electric bass distortion nut and i always like at least a little on it at all times now. but i can't even turn up a b-15 loud enough with my bands to get distortion so the vt is how i get it.
 
#9
banikek said:
Another question - when you plug an 8 ohm speaker into the "Ext. Speaker" output, are you also putting a "dummy" jack into the "Speaker"? That is what I was doing.
Click to expand...

Chris, short answer, no.

When I use an 8 ohm cab I use the ext. speaker jack as if it were the main speaker out, same as I would any other amp. As I read the schematic, (1968 model B25b by Joe Piazza) when the ext spkr jack (it's a switching jack) is used, it cuts off the 16 ohm main output, and switches to an 8 ohm tap off the output transformer. Also, my '69 model has an attached main output speaker cable with a 4 prong plug that only fits the orig 16 ohm cab. Yours is newer, may be '72 to '75? and I'm not sure if you have that set up or if it was modified.

BTW- I think that B-18 cab looks pretty neat, I often plug into an SWR single 15", no vintage vibe thing there.
 
#10
Hi,

I'm about to recive my Ampeg B-25B. At the back I see 16ohm out and I read that you can plug 8ohm into ext. speaker. But my cabinets (two Phil Jones Piranha 4B) are 8ohm each and I would like to use them both. I correct my previus question, so can I plug one 8ohm cab into ext. spkr. jack and the other in 16ohm? Would that result in 8 ohm for each out?

Thanks guys in advance.

Peter
 
Last edited:
#11
Hi Jens, I'm not sure that it would work using both output jacks as you inquired. The correct way to use both 8 ohm cabs would be to re-wire one of them with two jacks so they may be used together in series and the load would be combined and equal 16 ohms, then plug that load into the 16 ohm jack. It can be done by adding 2 new jacks to one of the cabs, that speakers + and - would each be connected to one of the "tip" terminals on each new jack, the "ring" terminals of the new jacks are connected to each other. These two new jacks are only to be used in a series configuration with your matching cab, and the jack that connects to the + speaker terminal must be the IN, it receives the cable from the amps 16 ohm speaker output jack, the other jack is used to jump from the first cab to the second cab. If not plugged in correctly, your speakers will be out of phase and your low frequencies will be canceled out. (phase cancellation)
So you have an IN and an OUT jack now, on one of the cabs, the other cab has not been touched. From the amp 16 ohm jack you plug into IN, the TIP term goes to the speaker +, speaker - then goes to the TIP term on the OUT jack, from the OUT jack, your jumper cable then connects to the input jack on the second cab, again TIP term goes to speaker +, speaker - goes to the RING term and is carried back through the first cabs OUT and IN jacks whose RING terminals are connected, and back to the amp. Thus your cabs are connected in series to the amp and you can safely run both cabs at a 16 ohm load.
Any other way you do it the two cabs will be in parallel and will result in a 4 ohm load. I have run my B25 head at 4 ohms into a 410hlf cab for a jam session now and again without issue, but I would not advise doing that often or for extended periods. The head was designed to be run into 16 or 8 ohms using the proper outputs.
 
Last edited:
#12
Hi,

my sound technician made me a cable in series so I plug it in 16 ohm channel and connect each plug in to my 8 ohm PJB Piranha 4B. That is solution for me and it works perfectly. No need for another cab or dummy jack...I'm happy :)

Here is link how it sounds with Radial JDX and G&L L2000 1983. I have all settings set straight 12 o'clock (at zero) and signal goes dierct form JDX to my laptop. So this is signal from vintage amp to PA.

 

Attachments

#13
Jens1 said:
Hi,

my sound technician made me a cable in series so I plug it in 16 ohm channel and connect each plug in to my 8 ohm PJB Piranha 4B. That is solution for me and it works perfectly. No need for another cab or dummy jack...I'm happy :)
Click to expand...

Or you could do that....so simple, wish I'd thought of it. :)

Sample sounds really nice, you'll have tone for day's with that rig!

You do have speakers or some kind of load connected to the amp though, even when recording direct right? 'Cause if not, things will go bad on you.
 
#14
vistacruiser said:
Or you could do that....so simple, wish I'd thought of it. :)

Sample sounds really nice, you'll have tone for day's with that rig!

You do have speakers or some kind of load connected to the amp though, even when recording direct right? 'Cause if not, things will go bad on you.
Click to expand...

Yes, speakers have to be connected all the time. This JDX box does not carry load, some DI's do, like Palmer PDI 03, which can be in 2, 4, 8 and 16 ohm. Radial JDX suits me better since is more portable in live situation.

Thanks about a tone...I feel happy with it. :)

There is one thing I'd like to try, that is REDDI, R. JDI, Countryman 85 or something like that + SE MD421 or EV RE20 on a cab... maybe one day...:D
 
#15
banikek said:
Many years ago I picked up an old, beat up Ampeg B-18 speaker cabinet. Almost all the tolex was gone and no amp was included. Since then it has gone thru a few incarnations and currently is loaded with a nice JBL 18. Today I picked up an Ampeg B25B head. Very clean. Paired up nicely with the old (now new) B-18 cab.

IMG_0921.jpg

IMG_0922.jpg


Did the plug trick on the back to fool it into 8 ohm mode. Also played around with crossing the channels etc. Sounded best with my old P bass with flats and also with an old Mosrite bass I have. Please let me know if anyone out there has some tricks or tips for me in regards to this amp. Should be fun!

Also, anyone ever use a B-18 with an upright bass? If so do you mic it or use a pickup?

thanks,
chris
Click to expand...

Chris,
Like Jimmy said in his earlier post, I can't imagine that your B-18 wouldn't sound great with Double Bass. Your B-25B is the head only version of the B-15S, which I played through on many occasions. Unfortunately,
when I gigged with a B-15N pickups were in their infancy.

Ric
 
#18
Guys,

last night on a gig sound from Ampeg b25b>JDX>PA system was really bad - too farty, distorted in bad way, nothing like day before I plugged from JDX to laptop (sound is in previous thread). I recorded it again today and sound is perfect!

So my question is why sound on PA from ampeg b25b to Radial JDX is so bad? What could be wrong? Is it that everything is just more transparent and you can hear sound all in all is not so good?

I hope you understand what I'm aksing...I'm from EU and I try to describe things the best way my english allows me :)

So any thoughts, ideas? Have someone experiance on that matter?

Thanks in advance.
 
#19
vistacruiser said:
Hi Jens, I'm not sure that it would work using both output jacks as you inquired. The correct way to use both 8 ohm cabs would be to re-wire one of them with two jacks so they may be used together in series and the load would be combined and equal 16 ohms, then plug that load into the 16 ohm jack. It can be done by adding 2 new jacks to one of the cabs, that speakers + and - would each be connected to one of the "tip" terminals on each new jack, the "ring" terminals of the new jacks are connected to each other. These two new jacks are only to be used in a series configuration with your matching cab, and the jack that connects to the + speaker terminal must be the IN, it receives the cable from the amps 16 ohm speaker output jack, the other jack is used to jump from the first cab to the second cab. If not plugged in correctly, your speakers will be out of phase and your low frequencies will be canceled out. (phase cancellation)
So you have an IN and an OUT jack now, on one of the cabs, the other cab has not been touched. From the amp 16 ohm jack you plug into IN, the TIP term goes to the speaker +, speaker - then goes to the TIP term on the OUT jack, from the OUT jack, your jumper cable then connects to the input jack on the second cab, again TIP term goes to speaker +, speaker - goes to the RING term and is carried back through the first cabs OUT and IN jacks whose RING terminals are connected, and back to the amp. Thus your cabs are connected in series to the amp and you can safely run both cabs at a 16 ohm load.
Any other way you do it the two cabs will be in parallel and will result in a 4 ohm load. I have run my B25 head at 4 ohms into a 410hlf cab for a jam session now and again without issue, but I would not advise doing that often or for extended periods. The head was designed to be run into 16 or 8 ohms using the proper outputs.
Click to expand...


As mentioned earlier, a series cable could easily be fabricated - no need to modify your cabs. Additionally, the term "ring" is being used here incorrectly and does not apply to a traditional quarter-inch speaker plug or jack. "Sleeve" is correct. I don't mean to be nit-picky, I just wouldn't want folks to go down an unfortunate path by trying to use a TRS plug or jack.
 
#20
Ric Vice said:
Chris,
Like Jimmy said in his earlier post, I can't imagine that your B-18 wouldn't sound great with Double Bass. Your B-25B is the head only version of the B-15S, which I played through on many occasions. Unfortunately,
when I gigged with a B-15N pickups were in their infancy.

Ric
Click to expand...


The B25B is closer to the B18 head. The B15S was two channel 12AX7 for the first gain stage on each, combined through a 12DW7, 12AU7 driver and 7027 power section with a solid state rectifier. The B25B was two 12AX7s with a 7199 phase inverter, 7027 power section, and 5AR4 rectifier, the power section is closer to the design of the B18N/B15Nc/d amps that used the same 7199/7027/5AR4 setup with 6SN7 preamp tubes.
 

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