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Double Bass Bandmates love my...B15N?!?!

Jeff Michael

Jeff Michael

Mar 15, 2001
134
185
55
Philadelphia PA
#1
I have been playing with a couple of retro blues acts for awhile. Since the volume level is usually fairly high and since the axe I take out for that work is my old patched-together American Standard, the purist notion of tone isn't at the top of my priorities list. So I've been using an Ampeg B2--a 200W solid-state amp driving a 15" speaker--running through an ART tube preamp (one of those $50 Musicians' Friend specials) to theoretically match the impedances. Or whatever.

So yet again the B2 has broken down. Out of necessity I've grounded it (and the preamp for superstition's sake) and rotated my loyal old 1960 B15N into active duty, purely as an emergency stopgap. I mean, the thing's only rated at, what, 25W? There's no way it's going to pull the weight, right?

Wrong. EVERYBODY I play with is marvelling at my 'new' tone. They all love how they can hear me perfectly well and how my sound has "articulation", "presence", "warmth". Somehow that little fliptop mouse is roaring.

This is maybe the second time that a sidelining of the B2 has brought the B15N onto the field...and come to think of it I seem to remember having the same sort of experience that last time too. So that settles it: I'm snagging another old B15 off of eBay ASAP and going back to my roots, baby.

Talk about an eye-opener!

JAM
 
#5
There is magic in the B15N Series and I think it comes
down to four things.
Tube amplifiers emphasize even order harmonics versus
odd order, giving them a more natural sound (engineers and
techies feel free to chime in on this one) I'm going from memory.
Evidently, when you hand trim the leads on resistors and capacitors
before soldering them to the board, like they did in the old days, each amp sounds slightly different, and supposedly that accounts for the
subtile differences between two amps of the same generation.
By, the time you get to the third generation of the B-15N (B-15NC) they were using "integrated circuit's" and "circuit packets" so that would also effect the sound, because these "circuit packets" were made by other manufactures for Ampeg.
The B-15 also had a double baffle system for the speaker which was
attached inner baffle with a 3/8" air space between the inner and outer
baffle's. That's unique to the B-15N series and to my knowledge no other
bass amp has ever used that cabinet design. When Ampeg changed the
design in 68' it changed the sound.

Thanks to Greg Hopkins and Bill Moore
for "Ampeg, The Story Behind the Sound"

Ric
 
#6
I played through a B18N for years. The original Goodman 18 was kinda floppy sounding so I replaced it with an Altec 421A 15". Great sounding amp for low to medium volume work. The chassis was beautiful inside- all neatly hand wired, gold stripe resistors, brass Carling switches, obviously built with much care. It came with a dolly that fastened to the underside of the cabinet with a big hand knob.
Wish I still had it...
 
#7
the B-15 was designed by two working bass players, one, Jess Oliver, an engineer and semi pro and the other, Everett Hull, a guy who had been a pro bassist in NYC and on tour with various big bands. Hull hated Rock and Roll--he was a jazz guy. There are stories in the ampeg book about Hull and Oscar Pettiford staying up late tinkering with amps. They were hi-fi geeks

Anyway, the point is that the B15 was the Hi fi, state of the art bass amp of its time. It was as good as tube audio was going to get, (which is pretty good--a lot of the same designs are still in production today) and it was designed by working pros for working pros, in studios and on stage.

I have a B-15 N, and it just always sounds good--warm and phat but clear and not muddy. I love the amp, but rarely use it to gig with, and it's obvious why--it's heavy as a broken heart and it's lacking headroom. But when people hear it they smile.

For the life of me I can't understand why no one has tried to capture a b15 sound with more headroom. Maybe it can't be done?
 
#8
You know, you could be on to something here. The B15 was build
at a time when 25 watt amps were "hi power". So, based on
the existing technology they built the best possible amp and
it sounded great and it still does. Could be,
that the portaflex cabinet only sounds good coupled with a lower power head.
They reissued the B15 with a solid state rectifier at 100 watts,
but their pretty pricey, and I haven't heard of anyone buying
one or endorsing it for that matter. :)
 
#9
The reissue was just not the same beast--it had a master volume control, which seemed really dumb to me, and I think--but I might be wrong--it had different power tubes. I played one it was definiely lacking what I liked about my b15
 
#10
Ric Vice said:
There is magic in the B15N Series
Click to expand...

Amen to that! I'm through denying it anymore. If a gig takes more than my B15N has to offer volumewise, somebody better drop a mic on it, 'cause I'm not going out with anything else.

I've heard tell that Larry Taylor says 25W is all you need.

Ric Vice said:
Thanks to Greg Hopkins and Bill Moore
for "Ampeg, The Story Behind the Sound"
Click to expand...

You may have heard me blow my own horn about this before, but my name's in there! I'm thanked, having sent them some info about my fliptop. It's a really early one, I reckon, having navy random flair tolex instead of the more typical blue check, and a 5U4 rectifier instead of a 5AR4. It's an odd duck in a lot of ways, to tell the truth.

JAM
 
#12
I actually own one. It's sitting in the garage because it
has a blown transformer and their are no longer any
replacement parts for it. In order to repair it you have
to have the transformer re-wound. So, I'm going to
treat my self to a rebuilt one as soon as I can find
somewhere to re wind that baby.

Ric
 
#13
Ric Vice said:
I actually own one. It's sitting in the garage because it has a blown transformer and their are no longer any replacement parts for it. Ric
Click to expand...

Mine's sitting in the garage as well - also with a blown transformer as far as I can tell. Does anyone know how readiliy you can find someone to rewind the transformer and how much it might cost?
 
#15
jstiel said:
I just did a Google search and did find a place in NY that sells parts. A new transformer is - gulp - $200.

[Invalid or Expired Link Removed]
Click to expand...

I'm actually surprised that you found one!!.
That's the price they were going for five years ago.
Since you found it, you really might want to consider
getting it. That B15 you have is a valuable amp even
if you don't want to use it.

Ric
 
#16
Ric Vice said:
I'm actually surprised that you found one!!.
That's the price they were going for five years ago.
Since you found it, you really might want to consider
getting it. That B15 you have is a valuable amp even
if you don't want to use it.

Ric
Click to expand...

I agree, I should get it fixed. I thought about this a while ago and forgot about it. It is a great sounding amp but that sucker is heavy! I'm going to call around here in the Detroit area and see if I can find someone to do the work.
 
#17
25 watts doesn't sound like much power UNLESS you feed it to a high efficiency speaker.

Some older speakers were astonishingly good because the magnets were really powerful. The magnets used to be made from AlNiCo - aluminium/nickel/cobalt - which could hold a tremendous amount of magnetism. Then there was a world shortage of either nickel or cobalt (can't remember which) in the 60's and no one could afford to make these magnets any more. It wasn't until around the 80's that they invented neodymium, which still isn't as good as AlNiCo, but coupled with other advances like edge-winding the coil wire and ferro-fluid damping has finally made the modern speaker better than its older counterpart.

So the old Ampeg rig may well be as loud as a modern one because the speaker converts more of the amp power into sound. Here's some maths:

Speakers are assessed for the sound power they produce by feeding them with 1 watt and measuring the output at 1 metre. 97dB/w/m is common. They can get as high as 106db/w/m however. An increase of 3dB is a doubling of sound as well as amplifier power. So... Take a 25W amp driving a 106dB/w/m speaker. To generate the same sound power into a 97dB/w/m speaker, you've dropped 9dB of speaker sensitivity, so it's 8 times less efficient. In other words, you need 200 watts to match the first combination!

Hope this helps.
 
#18
I think this information about magnets is really wrong--in the 60s they started using "ceramic" magents, which are much more powerful for their size than alnico and les prone to deformations under high power--I have a ceramic magnet jensen from a 67 ampeg jet. It's a very efficient speaker and much less prione to distortion. Weber speakers has a good FAQ on speakers and magnets at webervst.com. There are a lot of advanntages to ceramic magnets and they are STILL the norm in bass speakers--you can't use alnico in really high power application because it's too heavy. Neodymium speakers are a recent development in mass production-less than a decade as I understand it-the material was hard to make until recently
 
#19
Doug Ring said:
...Then there was a world shortage of either nickel or cobalt (can't remember which) in the 60's and no one could afford to make these magnets any more. It wasn't until around the 80's that they invented neodymium, which still isn't as good as AlNiCo, but coupled with other advances like edge-winding the coil wire and ferro-fluid damping has finally made the modern speaker better than its older counterpart.
Click to expand...

I think it was a cobalt shortage in the late '70s due to the element coming only from then "iron curtain" countries. Also, edgewound voice coils had been around for decades from JBL, Altec, and EV.

Take a 25W amp driving a 106dB/w/m speaker. To generate the same sound power into a 97dB/w/m speaker, you've dropped 9dB of speaker sensitivity, so it's 8 times less efficient. In other words, you need 200 watts to match the first combination!
Click to expand...

Good point, though 106dB/W/m speakers would be pushing the limit. Klipschorns, I think, were the efficiency kings at 104dB/W/m. Altec A7s were about 101dB/W/m. I don't remember too many cone drivers that exceeded 100dB/W/m. Modern drivers are probably several dB less sensitive than old ones, though.
 
#20
I was referring to smaller modern speakers, like 8 and 10 inchers and the GK 12". I don't really know what their efficiencies are, though. True too, the old cheaper jensens, CTS, Eminence, etc. used ceramic magnets, which were quite efficient. Come to think of it, I believe all the standard drivers used in the portaflex amps used ceramic magnets (which I believe is the same as "ferrite").
 

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