The Vox 60th Anniversary AC15HW60 Limited Edition Amplifier (2017)
Made in the United Kingdom

The fifteen watt JMI AC-15 was the first commercially
successful amp produced by Vox. Although originally introduced in 1958 as the "AC-1," it was the 1960 circuit redesign creating the AC-15/4 (15 watts/4 inputs) that ignited sales of the amp at Vox. Most of the bands of the early British Invasion, including the Beatles and Gerry and the Pacemakers, used AC-15/4 amps in their formative years.

JMI Vox AC-15/4 - "Point to Point" Hand Wired Circuitry
The circuitry of the JMI Vox AC15/4 featured "point-to-point" hand-wired construction on chassis mounted phenolic lug strips. Point-to point wiring implies that the leads of each electronic component are hand-wired directly to the leads of the next using the shortest possible signal path. There can be no printed circuit boards in an amp with point-to-point construction.

The design for the Vox AC15/4 circuit was published on JMI schematic OA/031 "AC15 Amplifier Circuit No 3," dated April 4, 1960.

JMI Vox AC15/4 - Normal Channel - EF86 Tube
While the preamp sections of most amplifiers were powered by dual triode tubes such as the 12AX7 and 12AU7, Vox lead engineer Dick Denney took a different path. He designed the Normal channel of the 1960 AC-15 to include an EF86 pentode tube. The additional gain stage offered by the pentode created the legendary chimey tone loved by generations of guitarists. The iconic "James Bond" guitar riff first heard in the classic 1962 movie "Dr. No" was played through an AC15/4.

When overdriven, the EF86 smoothly transitioned from clean to a sweet, musical distortion that was ideal for soloing. Denney so liked the tone of the EF86 that he also included it in the preamp designs of the Vox AC-4, AC-10 and AC30/4.

JMI Vox AC15/4 - Vib/Trem Channel
Many amplifiers include a simple effect called tremolo. The AC-15/4 featured the complex "Vibravox" circuit offering either tremolo or vibrato. While tremolo pulses the volume of the amp, vibrato varies the pitch of the signal. A two position panel mounted rotary switch selected either tremolo or vibrato and a three position panel mounted rotary switch adjusted tremolo speed. A single button "egg" foot switch remotely turned the effect on and off.

In an interview with Guitar Player magazine, Dick Denney admitted that he "reverse engineered" the complex Vox Vibravox circuit from a home console organ before incorporating it into the design of the AC-1 in 1958. Initially Vox was so protective of the Vibravox circuit design that they initially encapsulated a number of its key electronic components into a set of sealed modules. By the time the AC15/4 was introduced in 1960, Vox no longer concealed the seventy plus components comprising the Vibravox circuit.

JMI Vox AC15/4 - EL84 Powered Power Amp Circuit
The AC15/4 power amp was powered by a pair of cathode biased EL-84 power tubes. The EL-84 is a highly efficient tube capable of producing 15 watts per push/pull pair at a relatively low circuit plate voltage of only about 340 volts.

The efficiency of the EL-84 also had a downside. EL-84 tubes were a bit more prone to distort due to their reduced "headroom." Simply stated, when pushed hard, the distortion level could creep up into the 7 percent area. This distortion was normally controlled by the incorporation of a circuit design called "negative feedback." Negative feedback sends a bit of the signal coming out of the amplifier back to the input of the preamp. Negative feedback not only cleans up undesirable distortion, it also removes some of the pleasing even order harmonics from the amplifier output.

After listening tests, Dick Denney decided he preferred the harmonically rich tone and the natural sounding overdrive of the AC-15 amp when negative feedback was not employed. Although unconventional in design for the period, eliminating the traditional negative feedback circuit in the power amp made another major contribution to Vox tone.

JMI Vox AC-15/4 - Chassis
The design of the JMI Vox AC-15/4 chassis combined a pressed steel horizontal base with a "L" shaped vertical assembly made of aluminum. The steel base of the chassis supported the power supply and output amp sections of the AC-15/4. The power transformer and output transformers were located at opposite ends of the chassis base to provide proper balance. The vertical aluminum section of the chassis enclosed the preamp circuitry, shielding it from electronic interference from the transformers and power supply.

JMI Vox AC15/4 - Celestion 12" G12 Alnico Speaker
Originally introduced in 1936 for use in radios, a modified version of the 15 watt G12 alnico speaker was produced by Celestion for use in Vox AC-15/4, AC-30/4 and AC-30/6 amps. The earliest version of the Celestion/Vox G12 speaker was painted tan and had no magnet cover. G12 speakers produced for Vox from 1960 through 1964 were painted blue and had a stamped steel magnet cover. Later Vox G12 speakers were painted silver. All versions of the Vox/Celestion G12 used the H1777 cone, first supplied to Celestion by Pulsonics and later by Műller.

Vox AC15HW60 60th Anniversary Amp - 2017
Vox ended a 45 year tradition of producing amps in the UK in 2003 when production was moved from Milton Keynes, UK to Shenzhen, China. While many bemoaned the thought of Vox producing amps in China, this shift in production enabled Vox to slash the street price of the AC-15 by 40%. Yet, many longed for the day when Vox amps were made in the UK.

Introduced to commemorate the 60th anniversary of Vox in 2017, the AC15HW60 and the AC30HW60 were the first Vox amps to be manufactured in the UK since 2003. The images shown at shown at left highlight the design and features of the AC15HW60.

With it's steel base, aluminum upper section and slider board, the AC15HW60 chassis closely resembled the original AC15/4. The AC15HW60 featured point-to-point hand-wired construction and followed the original AC15/4 circuit design from JMI schematic OA/031. The Normal channel of the AC15HW60 used an EF86 preamp tube and the Vib/Trem channel included the entire original Vibravox circuit. Vox even included an original style "egg" foot switch sourced from North Coast Music.

Like the JMI Vox AC15/4, The 15 watt AC15HW60 power amp section was powered by two cathode biased EL84 tubes with no negative feedback. The AC15HW60 also featured a UK made Celestion G12 "Alnico Silver" speaker with a Műller H1777 cone.

AC15HW2 Specifications
Country of Origin United Kingdom
Tube Complement 3 -12AX7, 1 - 12AU7, 1 - EF86, 2 - EL84,
1 - EZ81
Circuit Construction Point-to point hand-wired on turret strips
Cabinet Construction 13 Ply Baltic Birch Plywood
Inputs Two Vib/Trem Input Jacks (High and Low)
Two Normal Input Jacks (High and Low)
Foot Switch Jack
Outputs Three Speaker Output Jacks
Controls Vibrato Speed, Vib/Trem Select, Vib/Trem Volume, Normal Volume, Brilliance, Cut
Speakers One 16 ohm Celestion G12 "Silver Alnico" with a Műller H1777 cone
Included Accessories Padded cover, "Egg" foot switch, Power Cord, Owner's Manual
Dimensions, Weight 20.98" x 10.94" x 22.64"
53 pounds
Retail Price $4299.99 USD
"Street" Price

$2999.99 USD



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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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