Portaflex Models

Loud has a good selection of Schematics, manuals, and literature available for their present and past products on their service web site.

B-15 Family(top)

A-15 1960(top)

A-15 1960

B-15 1960(top)

B-15 1960

B-15NA 1962(top)

B-15NA 1962

B-15NA/NB 1963(top)

B-15NA/NB 1963 (late) with Solid state rectifier, new style grille cloth.



B-15NA/NB note the larger sized octal speaker cabinet connector.

B-12N 1963(top)

The B-12 and the B-15 shared the same amplifier. The B-12N speaker cabinet is not a double baffle design, it is a has two oblong ports and a single baffle.



Note the unique plastic suitcase type handle that was on the 1963 amps. The cabinet had the same tilt back mechanism, seen in the lower center, as on the B-15N.



The octal speaker connector was still being used in 1963.



The plastic handle.

B-15NC 1964(top)

5AR4 tube rectifier, 4-pin speaker cabinet connector. See additional images of this amp here: All Original 1964 B-15N in Detail.

B-15NX 1964(top)

B-15NX 50W

B-15NC Column(top)

The B-15NC Column model came with a 50W B-18N head matched with a 215 ported cabinet. The same style cabinet was also offered with the BT-15 GT-15 transistorized heads. The cabinets came standard with CTS speakers, Altecs were optional.


1967 BT-15C 215 Column Speaker Cabinet


GT-15C transistorized with Altec speakers. Same cabinet as the B-15NC (column).

B-15ND(top)

The B-15NC (column) and B-15ND both were based on the 50W B-18N head and were matched with different cabinets. While the B-15NC column cabinet had two 15 speakers in a ported box, the B-15ND was a Portaflex cabinet with a 15 speaker. There was a 115 extension cabinet available so the cabinets could be stacked.


B-15ND. This cabinet was recovered and the grille cloth changed.


This is a 1964 B-18 head mounted on 1964 and 1965 double baffle cabinets with JBL speakers. It was assembled by ddbassGA and allows us to have a glimpse of what a stacked B-15ND would have looked like. Ampeg should have offered this combination, it's a great idea.




An assembled B-15ND.

B-15NF(top)

B-15NF 1966

B-15N 1967(top)

B-15N 1967

B-15N 1972(top)

B-15N 1972

B-15T(top)

B-15T

BT-15 1967(top)

1967 BT-15

BT-15C 1967(top)

1967 BT-15C 215 Column Speaker Cabinet

GT-15C 1967(top)

GT-15C transistorized with Altec speakers. Same cabinet as the B-15NC (column).

B-15R(top)

Jess Oliver's B-15R Design Recommendations for this model.


B-15R Same pre-amp as in the SVT CL, a unique power amp 100W/60W/40W depending on the tube configuration.


The B-15E extension cabinet is quite rare.


Front panel includes 0 and -15dB inputs, ultra-hi and ultra-lo selectors, and a half power switch.


Back panel features 6L6GC/EL34 bias selection, Speakon speaker connector, impedance selector. and balanced line out.

















Cabinet panel. The high frequency horn can be attenuated or turned off.


Crossover and wiring.


There is a light bulb on the crossover board that flashes as it limits surges and protects the horn.


Eminence speaker and high frequency horn.


View under the hood.

B-15S(top)

B-15S head


B-15S front


B-15S side

B-12XTC(top)

B-12XTC B-12XT head paired with a 412 cabinet

Heritage B-15(top)

There are different versions of the Heritage B-15.

In 2011, there was an initial run of 50 units that were built by George Metropoulos of Metropoulos Amps, a company well known for building plexi replicas. This model was not an exact replica of the original B-15N, but rather it paid tribute to it by adopting features from two of the most popular models, the 1964 B-15NC and the 1966 B-15NF. The channel 1 pre-amp is based on the 1964 model, the channel 2 preamp is based on the 1966 model. The power amp is switchable between the 1964 cathode and 1966 fixed bias designs. The power supply is stiffened by the addition of a choke and more capacitance. This provids less sag and Distortion and more headroom when the amp is pushed hard allowing the designers to get a little more out of the amp. Jess Oliver consulted on the amplifier revisions, and Mark Gandenberger of Vintage-Blue consulted on the double baffle cabinet design. The basic speaker cabinet is faithful to the original design. Mark guided them through a number of enhancements to the cabinet construction.


2011 Heritage B-15


2011 model in production




2011 Heritage B-15, under the chassis



In 2012, there was a second production run produced by a different builder of 100 amplifiers. There were a number of revisions made to the amplifier in order to meet the European Unions regulations. They include:


1. Nichicon caps are used in the power supply.
2. Signal path caps are from a different manufacturer.
3. All jacks have guards to prevent things from being inserted into the amp through the holes.
4. There are now five fuses instead of one. The main power fuse is in the IEC receptacle on the back of the chassis. There are four additional fuses on the back panel that protect the power supply. The standby switch no longer interrupts the links between the HT winding of the power transformer and the anodes of the rectifier. Instead, there are fuses in each link now and they’ve deleted the fuse in the HT rail. That accounts for 2 of the fuses on the back panel. The other two fuses are for the 5V rectifier heater and for the 6.3V heater circuitry.
5. The 6L6GC bias circuitry has been redesigned. There is now a single Capacitor and the component values have changed.
6. There are two instead of three toggle switches on the front panel, the 64/66 bias selection and standby switches are combined into a three position switch and there is a power on-off switch.
7. The power transformer, choke, and Output transformer are manufactured by Demeter Windings in the UK.
8. Blue LED lamps are now used for Ampeg logo illumination.
9. The turret board was layout was redesigned. Some changes to the ground points were made.
10. A DC 6.3V heater circuit was added. There is a piggyback board with a Full diode bridge and filter Capacitor.
11. Solder is 100% lead free.
12. Revised tube cage with elongated slots on the top for better cooling and white warning text.




2012 Heritage B-15


















DC 6.3V heater piggyback board








An enthusiastic review of the 2012 Heritage by Apex_speed.

Heritage B-15N(top)

Yet again redesigned to be more affordable. This version is based on the 2012 B-15. The chassis is no longer chrome, a printed circuit board is used instead of a turret board, and 12AX7 Tubes are used in place of 6SL7's. A very nice sounding amp.



Heritage B-15N

SB-12 Family(top)

SB-12 1966(top)

1966 SB-12, about as Clean as they come.


Ever wonder why the speaker is offset in the cabinet? By placing the speaker off center, it helps reduce resonances in the cabinet. Perhaps with the speaker that they used, this was necessary.




1966 SB-12


1966 SB-12 cabinet


For comparison, here is a B-12NC cabinet. Note the two oblong ports.

SB-12 1967(top)

1967 SB-12

SB-12 1970(top)

1970 SB-12

B-12XT 1966(top)

B-12XT 1966

B-18N(top)

1966 B-18N enjoying a day in the park.

B-18X(top)

B-18X

PF350(top)

Portaflex Series PF350

PF500(top)

Portaflex Series PF500

PF800(top)

Portaflex Series PF800

PF-20T(top)

Chassis gut shot:

PF-50T(top)

Chassis gut shot: