The history of the legendary Ampeg B-15

Ampeg B-15
(Image credit: Future)

Behold the Ampeg B-15, a simple box on wheels that houses the very crossroads of ingenuity, portability, and sonic superiority beneath its four latches.

When Ampeg introduced the B-15 Portaflex (short for portable reflex baffle system) in 1960, it set the standard for all future bass amplification, quickly becoming the most popular bass amp in the world.

More important, it gave the then-nine-year-old electric bass guitar its first true voice: fat and fundamental, thanks to the warmth of six tubes and a tuned, closed-back cabinet.

With the dawn of high-powered amps still a decade away, the B-15 could be found live and in the studio behind the instrument’s premier pluckers: James Jamerson in Detroit, Duck Dunn in Memphis, Chuck Rainey in New York and Los Angeles.

Through the ’70s, ’80s, ’90s, and into the new millennium, it has endured, much beloved and sought-after as a vintage piece, while permeating the studio plucks of such modern sharpshooters as Darryl Jones, Justin Meldal-Johnsen, Alex Al, and Owen Biddle.

Having turned 50, the latest chapter for the “the Flex” is the release of the Heritage B-15. To get the inside story of the ever-present Portaflex, we joined Tony Levin, Ampeg Artist Relations Manager Chrys Johnson, and Ampeg Senior Product Specialist Dino Monoxelos at the Massapequa Park, Long Island, home of Jess Oliver. A seminal figure in Ampeg lore, Oliver was the first person to put reverb in a guitar amp, helped design the vacuum form machine for the Ampeg Baby Bass, and hired Bill Hughes, the man behind the SVT.

His place in music history, however, is firmly cemented by his invention of the B-15. As Oliver was being presented with the new Heritage model he consulted on, he was more than willing to field questions about his fabulous fliptop.

How did you get into building instrument amplifiers?

Jess Oliver: I started out as an electrician, and I played upright bass on the weekends. I needed a pickup, so I went to Ampeg on 42nd Street and bought one from [Ampeg founder] Everett Hull. He was impressed that I could install it myself, and he offered me a job.

At the time, I was hanging 75-pound traffic lights on an extension ladder braced on power lines, so I took him up on his offer. He also paid for me to go to night school at the RCA Institute, to study amplifier technology and design.

The first amp I built was a Johnny Smith guitar model. Ampeg had the 825 and 835 bass amp line, and I built some prototypes around them that were an improvement, but I wasn’t satisfied with any of them until I designed the Portaflex.

Tony Levin: Where did that idea come from?

JO: Various sources—and from here [points to head]. There was an amp designed by Mitch Levine of the Premier Amp Company, whom I knew in passing. His came in two pieces, with a head that buckled to a separate enclosure with a sealed back.

I thought, if I design a closed-back cabinet that was properly tuned with ports and baffling, it would have the optimal bass response. The electronics portion came from the back of an RCA tube manual and what we had done on earlier preamps.

By shock-mounting the amp on top of the cabinet, I was able to reduce the vibration of the tubes and the chassis, also allowing them to cool better. Finally, for portability, I got the idea to turn the top over into the unit—like a Singer sewing machine I had seen—and attach a dolly to the bottom of the cabinet.

What bass players at the time were helping with feedback?

JO: All the members of the Manhattan Bass Club [a group of top session bassists who each bought an amp to be left at a studio so all of the members could avoid cartage].

Folks like Milt Hinton, Oscar Pettiford, and George Duvivier would come to the shop, as well as Latin players like Bobby Rodriguez and Julio Andino. Charles Mingus and [classical bass giant] Gary Karr, who both had Baby Basses and did ads for us, would come by, too.

And I’d attend studio dates to hear our amps— everything from a George Barnes album with 20 guitarists to a recording session with Elvis Presley, in which he listened to the pianist play the song once, and completely re-stylized it in his own way. I was also gigging on weekends, testing the B-15 and the Baby Bass.

TL: So you developed the B-15 mainly around the upright and Baby Bass?

JO: Yes, the upright and then the Baby Bass when it came out [1962]. We wanted a Fender for test purposes, but Mr. Hull wouldn’t allow it. For one, they were a competitor, but mainly because he hated rock & roll and loud music.

When rock bands like the Dave Clarke Five visited the factory, he would make me talk to them. Another time he saw a Gibson Maestro Fuzztone, and he was so angry he was stomping his feet, “Can you imagine? They’re selling distortion!”

When Ampeg started importing Burns electric guitars from England [1963], we smuggled a bass [EB-1] into the shop to use on amp testing. Later [1966], one of our amp techs, Dennis Kager, developed and patented the ƒ-hole basses [AEB-1 and fretless AUB-1], so we had those.

Tony, what’s your history with the B-15?

TL: It was the first amp I bought, while I was living in Rochester, New York. It sounded great, and it was a pleasure to be heard in large ensembles—although I was playing with Chuck Mangione, who would do concerts accompanied by an orchestra, and I remember the string players complaining that it was too loud!

When I got down to New York City in the late ’60s, I only had a Baby Bass and my B-15, and I quickly got a Fender because that’s what everyone wanted. Every studio had a Manhattan Bass Club B-15, although at that point they were unlocked and available for me to use.

Do you recall if you used one on any of your early notable recordings?

TL: Well, it was two or three albums a day back then, and a long time ago, but there’s a good chance I used it on record dates for folks like Buddy Rich, Lou Reed, Carly Simon, and Alice Cooper; I can confirm I used it on Mike Mainieri’s White Elephant [Just Sunshine, 1972] and John Lennon and Yoko Ono’s Double Fantasy [Capitol, 1980].

Jay Messina and Jack Douglas, who engineered those two albums, respectively, told me of modifications made to the B-15s at the Record Plant and the Hit Factory that added a pre- and postamp switch out of the back; Jack preferred recording direct with the post out, to get a bit more bite from the amp signal.

I also remember rock sessions where the engineers would turn the amp all the way up to add some distortion; it was a fantastic, crunchy tone that must be on hundreds of records from the era.

JO: You could get an overdriven sound by turning the volume knob past 11 o’clock, causing the amp to clip. I also designed in the ability to use two B-15s together with a regular q" guitar cable going from the rear external amplifier jack to either the external jack or the front instrument jack on the second B-15; the tone controls from the first amp would then work for both amps.

Jess, what was the thinking behind the B-12, the B-18, and the solid-state version of the B-15?

JO: The B-12[N] came out with the B- 15[N, in 1960]. It was the same head and power, with a tuned cabinet, but with a 12" speaker, so it was lighter and easier to transport.

The B-18 came a little later [1963]; it was the same head but with more power— it could reach 60 watts—and with a larger speaker and double-baffle cabinet. The solid-state BT-15 came just before I left Ampeg [1966]. It sounded very good, but I had an argument with Mr. Hull about the design; you could fry an egg on the head because the heat sink was too low.

Soon after you left Ampeg you founded the Oliver Sound Company, making instrument amps and PA systems, including the Powerflex bass amp.

JO: The Powerflex was larger and more powerful than the B-15. Ampeg had the patent on the fliptop, so I came up with a new design in which the head automatically lifted out of the cabinet using a small motor. I had about 28 employees by the early ’70s, and I had offers to go bigger, but eventually I decided to give it all up, scale back, and just maintain my amp-repair business here in my basement.

You were a technical advisor for the B-15R reissue, in 1997.

JO: Yes. The amp sounded good, but it was an infinite-baffle design, which sounds a little more hollow than the thick, doublebaffle sound of the original B-15. The Heritage B-15 has a double-baffle cabinet and it’s tuned perfectly. The usual hump you had at low or Ab is not there; it’s nice and smooth and even across the whole spectrum. That’s what I had in mind.

TL: Did you recommend any changes to your original design in your role as consultant on the new Heritage B-15?

JO: I advised adding a filter choke, which they did. I didn’t know enough at the time to add it on the original; the schematic from the back of the RCA manual didn’t have any choke on it.

But I’ve repaired many different brands of amps since, and the good ones all have chokes. It enables more power from the transformer. Originally, I used a 40Ω resistor to do the same thing, but I was wrong. It’s corrected now; George Metropoulos did a fantastic job of building and wiring the new version.

TL: What’s truly amazing is you used regular materials but made a great-sounding, indestructible, enduring product that is viewed as the holy grail of small bass amps.

That said, Jess, how do you feel having shaped the course of how modern music sounds?

JO: All I can say is I’m very happy and extremely honored to have had a part in it all.


Groundwork for the Heritage B-15 began when Ampeg’s Chrys Johnson chatted up George Metropoulos, owner/operator of Metropoulos Amp Inc. (which rebuilds and offers rebuild kits based on various vintage amps) about classic Ampegs and the Heritage line.

Ampeg Director of Musical Instrument Amplification Pyotr Belov had further discussions with Metropoulos about a reissue B-15, and at Winter NAMM 2010 the ball got rolling. Jess Oliver became the chief consultant, and at his recommendation, Mark Gandenberger of Vintage Blue (which builds reproductions of the original Ampeg B-15 double-baffle cabinet) was brought in to consult on the cabinet construction. We asked Metropoulos for insight into his rockin’ rebuild.

How did you go about trying to replicate the B-15 sound?

I started by listening to several original examples, and it became clear that while each sounded slightly different, they all had an unmistakable B-15 tone. I tried to capture that unique tone and feel in every way.

My goal was to have the Heritage B-15 react like the originals, whether running clean and punchy or fully saturated with the channels dimed. Ultimately, players should have the same overall experience playing this amp as they would playing a vintage one.

What do you feel were the key ingredients to the original’s great sound?

Definitely the cabinet and double baffle, which Mark and the team who developed the new cab did a fantastic job on. From my end, the transformers were a big part, which we had to replicate from scratch. The tubes are key also; 6SL7s are octal dual triodes, and they have a distinct American sort of sound.

We had to source new-old-stock military versions to capture the sound of the originals. Another key factor is the circuit. Early on, the tone controls were placed after the first preamp gain stage, and later Jess moved it to after the second gain stage.

This affects how the tone stack is driven and how the channel compresses and saturates. We duplicated these circuit topologies with the ’64 [B-15NC] channel and the ’66 [B-15NF] channel on the reissue, as these were deemed to be the most coveted versions of the amp.

Were any other upgrades or modifications made?

Jess favored adding a choke, so that was on the drawing board at the beginning of the project. Technically speaking, the choke is a coil, part of the power supply, that acts as a filter in conjunction with the capacitors.

It contributes dynamically, as well, charging and discharging to meet the supply demands of the amp as you play. Simply put, it feels a little different, but in a desirable way. The speaker was custom-designed by Eminence. Ampeg gave me full artistic leisure to source or make the most accurate parts possible for this amp.

I prototyped and compared and listened critically to the protos vs. original B-15s made between ’64 and ’72, eventually settling on the complement of parts and values you see in the Heritage B-15.

B-15 timeline

1956 Jess Oliver is hired by Ampeg; gets idea for B-15 circa 1958
1960 First B-15 Portaflex introduced (for $355), with single-channel 25-watt head; replaced within eight months by the B-15N (N for “new”), which features two channels and a Jensen speaker; B-12N (25 watts) also introduced
1961 A tilt-back rod (until 1964) and light-up Lucite logo (until 1968) are introduced on the B-15N
1962 Solid-state rectifier and blue check covering are introduced via the B-15NB
1963 B-15NL designates a JBL speaker upgrade; 50-watt B-18 introduced
1964 B-15NC returns to a tube rectifier; B-15X introduced, with horn tweeter and two 4" “echo” speakers
1965 B-15NF switches to CTS speaker, fixed-bias tubes, and single-baffle cabinet; 25-watt SB-12 (SB for “string bass”) introduced for use with Baby Bass
1966 Solid-state 50-watt BT-15 introduced, followed by BT-15C (2x15 cab, 85 watts), and BT-15D (100 watts); B-15NF raised to 30 watts; B-15X raised to 50 watts
1967 B-15NC “second version” (C for “column”) has 50 watts and a 2x15 cabinet with CTS or Altec speakers; B-15ND has 50 watts, 1x15 and a 1x15 extension cabinet; blue check covering on all models replaced by black covering and chrome trim
1968 Completely revamped B-15N “second version” introduced, 50-watt, two-channel head with new preamp, ultra-hi and ultra-lo inputs for each channel, and Thiele porting design
1971 Two-channel 60-watt B-15S introduced, based on the Ampeg V-4 head (offered until 1977)
1972 30-watt B-15N reintroduced
1973 Change to Eminence speaker, with Altec speaker as an option upgrade
1975 Grounded power cord added, polarity switch removed
1980 Final year of first 20 years of B-15 production
1986 B-15N returns to production
1988 B-15T introduced, with solid-state 100-watt head, twin triangle ducted port, and Electro- Voice speaker option
1997 B-15R reissue introduced with all-tube 100-watt head, B-15E extension cabinet, and diamond blue check covering
2006 Final year of second 20 years of B-15 production
2011 Release of the limited-edition Heritage B-15 (50 units)

Flip-top fans: B-15's famous fans speak up

Will Lee: “Wow, the B-15— the stalwart of the studio. When I broke into the session scene, all the studios had ’em, with a lock and chain around them and MANHATTAN BASS CLUB stenciled in white—although I was always able to use them. At that point, they were mostly for monitoring and pretty much had to be turned off when the red light came on to prevent leakage in the live room.

I was a DI guy back then, but I used the amp for tuning, jamming, and working out ideas, as well as live in the clubs. Later, they were used as recording amps until the mid ’80s, as bassists realized the B-15 was a great way to get a big amp sound by isolating it and putting a mic in the ‘sweet spot’ through proper placement. Thanks, Jess Oliver, for looking out for your fellow bassists and innovating such amazing gear as the B-15 and the Baby Bass!”

Bob Babbitt: “The B-15 was the amp I owned and used live and in the studios in Detroit, and later in Philly and New York. In Nashville, when they mic a live amp, it’s usually the B- 15; I used one on recent recording projects for Peter Frampton, Rod Stewart, and Phil Collins.

“They remain in studios to this day because younger producers, engineers, and bassists love the sound, whether they’re recording something old school or contemporary music. The B-15 is a timeless bass amp with a timeless tone.”

Chuck Rainey: “From 1962 to 1982, the B-15 was my main amp; that includes all gigs, films, and many recordings. In the New York studios, most of the amps owned by the Manhattan Bass Club were B-15s or B- 12s, and as a member, I provided one.

“The amps were usually placed on some kind of stand or support system, miked or with a direct signal taken from the back of the amp to the board. Many engineers and bassists preferred the B-12 because it was smaller and not as loud as the B-15, and it had a specific and even bass tone. Both amps were terrific and a big part of my career and my sound.”

Marcus Miller: “When I started on the New York session scene, the B-15 was the bass amp you saw in every studio. By 1983 or so, you stopped seeing them; bass players were recording direct by then. But I did a lot of early sessions using a B-15.

“If you listen to Luther Vandross’s Never Too Much album, you can hear it. Engineer Michael Brauer made a little ‘house’ for the amp, from baffles and blankets, so the sound wouldn’t leak into the other instrument mics. I think engineers liked the warm, tube-y sound of the B-15, combined with the small, unobtrusive size.”

Jerry Jemmott: “I used the B-15 both live and on sessions in New York, usually with an 80/20 blend of direct and miked amp sound in the studio. I wasn’t a member of the Manhattan Bass Club; I had to roll mine in and push theirs out of the way.

“Paul Roland Martinez (who played on ‘Hey Leroy’ with the Jimmy Castor Bunch) and I had our own little stash of B-15s and B-18s in selected studios. It was a brilliant, portable combo design with a great, tight sound.”

Sean Hurley: “I’ve been using my B-15 on almost every recording these days, except the most distorted rock tracks— although I recently drove the heck out of one on a session for producer John Shanks. What a glorious sound!

“It’s the perfect recording bass amp: It doesn’t need to be loud to get a killer tone, and is easily tucked away in a closet or isolation booth. With a flatwound-strung bass it’s old school, and with roundwounds it’s as modern as anyone needs. Pure bass tone that records with almost no effort, no unwanted frequencies to cut, nothing to be added—Jess Oliver got it right! The B-15 has stood the test of time.”

Justin Meldal-Johnsen: “I use the B-15 when I need a punchy, sweet, natural tone—which is most of the time, in fact. Sonically speaking, I just find it so consistently rewarding. The amp seems to provide the perfect spectrum, with the right amount of ‘note.’ It’s midrangy, without ever being ‘pokey’; it’s deep without being flabby. Even on some big rock recordings, I’ve found it well suited for a surprisingly big sound.

“Historically, I think the platform was amazingly well conceived and forward-thinking. There’s nothing like it, nor will there likely ever be.”

Darryl Jones: “The B-15 has always been a part of the studio experience for me. They were ever-present in all the studios I worked at in Chicago, New York, and L.A. No matter what kind of music you were recording, from R&B to jazz to rock, you could always find a suitable sound through it.

“In recent years, even with all of the other choices available, the B-15 has become more coveted, and now it’s exciting to see the release of the Heritage B-15. I hope I’ll be doing sessions for many years to come on both vintage and new models. Thanks, Jess Oliver and Ampeg, for getting it right from the jump.”

James Jamerson: According to Standing in the Shadows of Motown, Jamerson used a B-15 live (and occasionally in the studio), sometimes with an extension cabinet; the amp would be set with the bass knob all the way up and the treble knob on half.

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Chris Jisi was Contributing Editor, Senior Contributing Editor, and Editor In Chief on Bass Player 1989-2018. He is the author of Brave New Bass, a compilation of interviews with bass players like Marcus Miller, Flea, Will Lee, Tony Levin, Jeff Berlin, Les Claypool and more, and The Fretless Bass, with insight from over 25 masters including Tony Levin, Marcus Miller, Gary Willis, Richard Bona, Jimmy Haslip, and Percy Jones.