Ampeg B-15N questions

[JIO]

I recently acquired a 1977 Ampeg B-15N in good working condition. It is the first tube amp I've owned and have some related questions. When played at volume level around 10:00 (on the amp, w/B&T at 12:00) it sounds great. Not that loud, but rich in tone. If I turn it to 12:00, the speaker distorts on the lowest notes- kind of a blurty sound, and depending on the instrument, all the notes slightly distort if punched (regardless of BN&T settings). I know it only has 30w power, but I need to know if this is normal for this amp. The speaker is original and has a very thick slightly textured cone. I checked as best I could and there are no tears or damage. Notes/tones in the higher register are fine unless punched, it's mainly on the lowest notes-and this is on a 4 string. I doesn't matter if it's a passive or active bass, both will cause the distortion of tone. This is not a good distortion, but it sounds like the speaker is being pushed/overloaded, which seems strange considering the low wattage and the 15" speakers beefiness. I owned a Polytone 15" 100w combo transistor amp, and could do 12:00 w/no issues. If it just comes down to the low wattage, I get it- but why even have a knob that goes to twice an unusable level at all? Maybe all stupid questions, but help educate me. Thanks in advance. GEO

[coreyfyfe]

By about noon on the dial both of my B-15s (earlier versions than yours) would definitely be starting to break up, although certainly a more harmonic and less farty sound than you are describing. At that point, I would definitely say it should be starting to distort, but like I said your description sounds more like you're bottoming out the speaker than getting tube distortion. How are you eqing the amp? Your bass? If it's a 70s model you should have the thiele cab, which I believe are supposed to have more bass than earlier models.

[JIO]

This 77 cab has a full length 2" horizontal port at the bottom w/a floor-board above it and just below the lower end of the speaker w/a 2" gap at the back. Maybe this is the 'more bass' cab you speak of. I do all eqing at the bass, w/no boosts between. I'm not sure if it can be called harmonic distortion but you can still hear the clear bass tone but it has an additional cone vibration which I'm calling 'blurting'. I would have to think that playing at this level would damage something yes? I'm happy to use it for all that tube tone recording, but may not want to play it live unless it was a really low volume gig. Do you use yours live and what setting do you use? Thanks again.

[fu22ba55]

I have the same amp. (A late 70's B15N. Not 100% sure of the year.)

Mine gets nice and wooly around noon. That's why I bought it. I love the sound it gets when the power tubes start to distort. But I would also describe it as more "harmonic" distortion. Pleasing to the ear. Like a *really* nice fuzz pedal.

Do you have another cab you could try it with? If the speaker is original, it's possible you have an issue with the driver. Mine's long since been replaced with a late-model driver.

I don't use it much live since it won't get loud enough for my current needs, but plenty of folks do. JimmyM will chime in here in a minute and welcome you to the B15N club.

[coreyfyfe]

I've been using mine live more often lately. I've been playing with this singer/song-writer type group (acoustic, lead electric, keys, drums, percussion, bass) and we either have good PA support or have been playing small enough rooms that the B15 (angled toward the drummer and myself) is enough juice.

Like I said, your description definitely sounds like too much bass (or too much something) into the speaker, and not like tube distortion.

[JIO]

I'm hearing good news- maybe there is an issue I can resolve to get that nice fuzz you speak of instead of blurt. Is what you state as 'driver' in the speaker? What does it generally cost to address this? I have had work done by A Brown Soun here in the Bay Area so would probably take it to them. Thanks!

[coreyfyfe]

In this case, driver = speaker.

[JIO]

I ran the Ampeg head through another 15" Carvin PA cab and it sounded about the same. Not what I would call pleasing fuzz, more of a speaker/driver break-up sound.

[fu22ba55]

To my (limited) knowledge, Jensen C15N and P15N are common replacements for this box.

I have a C15N in mine, and I absolutely LOVE it.

I'm sure there are more schooled B15N guys here who will swoop in with better suggestions for speakers... I imagine over the years there have been some super-secret weapons in this box that will sound great... I don't know what they are. I'd wait for the hardcore B15N guys to chime in.

But I imagine you would have lots of choices... since you only need a driver that can handle a 30 watt amp, there are probably a lot of good candidates out there.

[fu22ba55]

Originally Posted by JIO

I ran the Ampeg head through another 15" Carvin PA cab and it sounded about the same. Not what I would call pleasing fuzz, more of a speaker/driver break-up sound.

Hmmm....

Sound clips might be helpful here too. Perhaps there's something screwy with the head itself.

(Or perhaps you're just not digging the Ampeg tone... but it's hard to tell. Something could be wrong with the head.)

I'll say this... my B15 definitely prefers passive basses, so maybe try troubleshooting with the passive ones first, then work your way back up to the active basses?

I vote for sound clips, or finding a local tech who can go over it for you. They're awesome sounding amps... indispensable in the studio, so I'd make sure it's 100% sorted out before you make a judgement on it.

[fu22ba55]

It could also be a bias issue. (Many tube amps need to be biased, while SS amps do not.)

There should be an army of crusty-old-tube-amp guys along here any minute to help troubleshoot. But if it's the head, it could be one of 100 different things... Most of which are usually fixable.

But a quick youtube vid of you you fiddling with the knobs and reproducing the unpleasant sound would help them troubleshoot for sure.

[JimmyM]

Originally Posted by fu22ba55

To my (limited) knowledge, Jensen C15N and P15N are common replacements for this box.

I have a C15N in mine, and I absolutely LOVE it.

I'm sure there are more schooled B15N guys here who will swoop in with better suggestions for speakers... I imagine over the years there have been some super-secret weapons in this box that will sound great... I don't know what they are. I'd wait for the hardcore B15N guys to chime in.

you rang?

sounds like everything's working fine to me. the reason the knob goes into distortion like that is because that's the way tube amps work. beyond their clean power, they can have double or more of peak (distorted) power. if you don't like it, keep it down. but sounds to me like you're getting full power.

the 77 b-15n came with either an eminence speaker or an altec 421a. the 421a is probably the best for this cab, although a lot of folks do like the darker tones of the cts and eminences they used. but the 421a will give you a little more upper mid and treble, which the thiele cab b-15's could probably use. it's got a strong low mid, probably the best in the business, but a little suppressed in the upper mids, so the altec should straighten that out. you have to buy them used, but they're plentiful on ebay.

[JIO]

How would I discern which speaker it is? It has no brand/type marking. It has a 5-3/4" square by 5/8" thick magnet wedged between two square solid metal plates. On the back of the top plate are the #'s 580154-1 and under that 67-7510. The metal housing is silver in color and the coil at the center is orange/brown. I didn't take the front cover off so I'm not sure what the face looks like.

[JIO]

I just figured out that it's an eminence speaker, and from the 7510 # was made in 75 (not 77)

I saw a matched set of Altec 421A 15's that have been rebuilt and uprated from 100 to 150watts [35hz-8000 hz / 97dB sensitivity] on ebay for $339 + 58.56 shipping ($397.56 total) from Dusty's Speaker Reconing. I don't need 2 and frankly don't have the scratch but will keep on the lookout for the Altec.

Thanks for your insights. How do I join your Portaflex club?

[JimmyM]

you can find them cheaper. be patient. or you may find you like the eminence just fine once you get sorted. many people do stick with them.

anyway, to join the club, post in the portaflex club thread, tell a little about it, maybe post a pic if you have it, and done.

Official Ampeg Portaflex Club Part III: Don't Stop 'Til You Get Enough

[JIO]

or it's a CTS, I saw a 70 on ebay that looked very similar w/similar numbers

[JimmyM]

nope, it's eminence. 67 is eminence's manufacturer code and cts is 137.

[fu22ba55]

Originally Posted by JimmyM

you rang?

I did.

So do your Spidey senses tingle whenever someone asks a B15 question, or do you just see the JimmyM signal in the skies above Apopka?

[pfschim]

OTOH, this kind of distortion is what you can expect from a low power amp like the B15N. It has some very reverential supporters here on TB and the rest of the bass universe, but it is just 27-30w, and not known (now or ever in the past) for having ANY clean headroom.

But it is a piece of bass playing history.

Now, where did I park my Fred Flintstone car, I have to "run" down to the Dino Diner for a brontosaurus steak with Barney.

[JimmyM]

Originally Posted by fu22ba55

I did.

So do your Spidey senses tingle whenever someone asks a B15 question, or do you just see the JimmyM signal in the skies above Apopka?

HAHAHAHAHA!!! that is hilarious! i saved it and i may make it my new icon!