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Background
When the first commercially released electric bass guitar came on the music
scene in the early 1950's it was like an unlit stick of dynamite. This new bass
instrument was capable of blowing up most amplifiers made at the time with its
wide dynamic range and powerful output. The early electric bassists, limited by
archaic amp technology, could not have known that their new instrument would
soon be shaking concert halls and vibrating listeners to the very soles of
their feet. Enter Jess Oliver, bass player, amp designer, and former vice
president of Ampeg.
 Soon
after arriving at Ampeg, Jess designed and patented the early 1960's Ampeg
A-15, B-12, B-15, and B-18 Portaflex "flip-top" bass amps. These groundbreaking
amps allowed bassists to finally hear themselves, and soon became very popular.
The amps put out full, rich, room filling tube tone with respectable volume.
Jess's designs combined reliability, innovative features, and compact size
making for a winning package. Today these Ampeg combos are still considered by
many to be the "definitive" bass amplifiers.
One of the Portaflex amps unique features was a handy storage method for the
amp head which was attached to the speaker cabinet: simply unlatch the amp
section from the speaker cabinet and flip the amp section over, exposing the
controls for use. For transport merely flip the amp section back over placing
the controls neatly inside the cabinet and re-latch the amp to the cabinet. A
removable four-wheeled dolly made transporting the amp a breeze.
A testament to the endurance and popularity of Jess Oliver's Portaflex amp
design is the fact that most major recording studios have a B-15 or B-12 on the
premises at all times, either by ownership or rental. One particular studio
instrument rental company in L.A. has a roomful of B-15's; each installed in
Anvil cases ready to be carted to the many world-class studios on the West
Coast.
The following interview with Jess Oliver took place in
June 2002.
When did you get started designing amplifiers?
I got out of the army (303rd A.S.F. Band) in 1946 and became an electrician
while playing bass in clubs at least three nights a week. I built a Karlson
Speaker enclosure (kit) and bought a Brentwood 15 watt P.A. amp and one kind of
pickup or another: DeArmond, crystal mike cartridge, etc., but was unsatisfied.
How did you come to meet Everett Hull, who started Ampeg?
I went to Everett Hull to buy an Ampeg (pickup) for my upright bass. He asked,
"Well, where's your bass?" He wanted to install the pickup for me, but I told
him that I could do it myself. He said I was the only bass player he ever met
who offered to do that, so he offered me a job. By this time I had a fairly
successful vocal group, working in some smart, east side supper clubs, radio
shows, and some on-the-road bookings. Sometime (months) later, my group broke
up. I looked up Hull. He had moved from Manhattan to Sunnyside, Long Island; I
took him up on his offer.
What was the first amp you designed?
The first amp I designed was the Johnny Smith Model, on Johnny's request.
Garage bands were beginning to bloom all over the country; we were both
interested in building amps for guitars, accordions, or anything. The next
thing I worked on was the Mercury Model. We needed a bigger place so I found a
larger factory in nearby Woodside.
What was the first bass amp you made for Ampeg?
We were still making the 825 & 835 Bassamp models when I came to work at
Ampeg. After I had the Woodside Factory all set up with benches, electrical
facility test equipment, etc., I started working on Bassamp prototypes. Hull
was happy to pay my tuition, so I enrolled at RCA Institute night school. I
ended up designing the A-15 & B-15 amps, which were well received. By then
I had learned to hide my prototypes until pre-production was started, so Hull
wouldn't sell them. They were only 25 watts, and had Jensen P15N speakers, but
they sounded much better than prior models.
Did you have any input from famous bass players when designing the Ampeg bass
amps?
We had input from many famous players. Hull always felt free to sell retail
sometimes because he had to, just to make the payroll (most manufacturers do
not sell directly to retail customers). We had all the bass players (as
customers) because nobody else made a practical upright bass pickup.
What particular electronics design or type was used for the Portaflex combos?
I believe I got the design for the Portaflex amp right out of the back pages of
an RCA tube manual; that is for the power amp. For the preamp I used the
circuitry common to some of the earlier models. (Tube manufacturers, in order
to increase sales, would sometimes provide manuals for making circuits to be
used with their tubes.)
Were you aware at the time that bassists needed more power to compete with the
electric guitar?
I was aware of their need for more volume but we were under capitalized. We
could only make the amps bigger, not more powerful. For instance, before the
B-15 amp, we had made a few 835 amps with a double fifteen-inch (side by side)
speaker cabinet. At this point, because of the Beatles and the garage bands, we
concentrated on guitar amp production. Besides, Hull did not approve of loud
music.
What make of bass guitar did you use to test your Portaflex series?
We didn't have an electric bass (horizontal) in the shop. At that time a
"regular bass" was an upright bass. Now, of course, a bass guitar is a regular
bass. I was talking with Dennis Kager, (a long time friend from Ampeg)
recently, and he recalls that even when we were at the Dalziel Road plant in
Linden, NJ, Hull wouldn't allow a "Fender" bass in the factory. It wasn't until
we started importing the Burns (brand) bass guitars that we had an electric
bass in the shop. On page 90 of the Ampeg history book recently released there
is a picture of Dennis using that bass (Burns) in the Quality Control Dept. of
Ampeg.
I've seen your Portaflex bass amps listed as B18N, B15N, B12N, B15ND, B12X,
B18X, and A15. What do the N, ND, X, and A stand for?
Model A-15, the A stood for Accordion. It was the same as the B-15 but
accordion players liked to be assured it was designed for accordion. The B-15,
B was for bass. The B-15N, the N stood for new engineering changes. The B-12X
and B-18X, the X stood for extra power or extra effects like reverb or vibrato.
As for the B15ND, I think that was the same circuitry only made with a printed
circuit instead of an eyelet board. I'd have to dig up the schematics to
confirm that.
Why do your bass amps sound so different than other amps of the same period?
I think Ampeg amps were and still are better because they were designed by bass
players. Back then we had a lot of input from customers that helped guide us.
The main reason Ampeg made a better bass amp was in the reflex enclosure
design. I don't remember Fender having anything but open-back enclosures or
infinite (closed-back) enclosures at the time.
What are the benefits of re-coning the 8-ohm speaker in Portaflex amps with a
4-ohm kit, as you did with my B-18?
After being in the amplifier business for many years, I found out you don't
always have to follow the book rules. When it comes to speaker load on a tube
amp, I've found you can load a tube amp down to saturation without damaging the
amp. You just get more effective power out of the amp. Just as long as the
secondary of the output transformer "sees" a path, some resistance, it doesn't
matter how low that resistance is, as long as it sounds good, and four ohms is
not below the saturation point.
When someone sends you a vintage Portaflex for a checkup, what do you check?
On repairing all the vintage amps I get, I sometimes replace the coupling
capacitors, filter caps, and off value resistors if needed. Tubes, of course,
if needed.
Are there any modifications that you suggest for increasing power?
I do suggest a solid -state rectifier, instead of a tube, which increases the
power and reduces the heat. Another improvement is replacing the speaker with a
Premium Quality speaker with an edge wound voice coil. This greatly increases
the effective power. Using a 4-ohm speaker instead of an 8-ohm does much the
same.
What about changing the existing 7027A power tubes to 6550's?
I've found that the new Sovtek 7027A tubes are great. If you can afford to
replace the 7027A's with 6550 tubes so much the better. Unfortunately, I didn't
leave enough room between the tube sockets on my Oliver brand amps to fit
6550's, which have bigger glass bottles.
Are matched power tubes important?
Matching the output tubes is very important. One of the most obvious benefits
is it eliminates the 120 cycle hum. Checking the bias voltage and adjusting if
necessary is equally important.
Do you suggest converting amps with an older two-prong plug to a 3-prong
grounded power plug?
I recommend using a three conductor grounded line cord, especially if my
customer complains about getting a shock.
 Did you have anything to so with the design of the Ampeg SVT
tube bass amp series?
About all I had to do with the SVT was to hire the man who designed it. His
name is Bill Hughes, now V.P of Technologies at Fender. Also, I helped conceal
the development from Hull, as he was so against rock and roll or any loud
music.
Your own Oliver amp company (not currently in production) made bass amps with a
very unique design: the amp section was made to electronically rise out of the
cabinet! Tell us about the Oliver amp?
When I left Ampeg, I was forced to go about getting my amp (The Powerflex) out
of the speaker cabinet in a different way than the Portaflex (Ampeg owned my
patent for the Portaflex). So I bought a sewing machine motor, took it apart,
brought out the field wires to make it reversible, and designed the elevator
mechanism to raise and lower the chassis in the cabinet. This made my Oliver
cabinet somewhat larger, since I couldn't invert the chassis, like the
Portaflex, making the power and output transformers flank the speaker magnet,
making it more compact.
What was the difference in the Oliver bass amps and Ampegs that you designed?
The larger cabinet and the increased power (60 watts instead of 35 watts) made
my Powerflex sound better than a B-15. I heard that Hull had a friend buy one
from one of my dealers, just to make the comparison. That's when Hull "threw
the baby out of the window with the bath water;" he made the B-15N larger, the
same outside dimensions as my Oliver amp, losing the compactness of the earlier
Portaflex model. The compact version of the Portaflex is still, to this day,
the more desirable, and usually brings a higher price.
I recently saw one of my Oliver Powerflexes on Ebay. It was being sold as-is,
and needed repair. I grabbed at the opportunity; who could better repair it. I
had a little competition from a music store in Florida, but I bid high and got
it for less than $500.00. I've since restored it; though I can't carry it
anymore but it's fun to look at! It sounds great too! It's the guitar model,
P-502 -one channel with reverb and tremolo for guitar, and the second channel
for bass.
Are you still consulting for any amp companies?
Ampeg still calls me in as consultant. They also bring me to the major trade
shows. I think that since Saint Louis Music bought what was left of the
company, Eugene Kornblum and the rest of his crew have done a fantastic job of
restoring the image of Ampeg.
It must be satisfying to know that your bass amps are still considered the
finest made, and that they continue to be used by pro studios and major
artists?
I'm extremely gratified, especially so by your last question. I really don't
know how to answer it, only that I'm honored by your asking. All I can say is
yes.
Jess Oliver lives in the New York area. He is also available for amp and speaker
consultation, and is currently taking in amps and speakers for repair. He can
be reached at his New York shop via email or phone at:
Oliversoundco@aol.com or tel. 516-799-5267
Please call before 5PM eastern time.
© 2002 Keithrosier.com
No part of this interview may be copied or distributed without expressed
written permission from Keith Rosier.com
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