JMI Vox UL 760 Amplifier





The serial plate from the first UL 760 amp Vox produced: Serial 1001.
This amp is part of the North Coast Music Vox amp collection


Close up view of the illuminated panel lamps


Three Button Effects Foot Switch


Reverb pan from a UL series amp. The red device connected to the
end of the reverb spring is a Sonotone 2T crystal phono cartridge


The UL amps had two wooden support rails rather than individual feet

Specifications - UL 760 Amp
Output Power 60 watts RMS
Tube Compliment 1 - ECC83, 2 - KT88
Channel One
"Vibrato Channel"
Two inputs
Boost switch
Volume
Treble
Middle
Bass
Vibrato Depth

Vibrato Speed
Foot Switchable Distortion
Reverb
Channel Two
"Normal Channel"
Two inputs
Boost switch
Volume
Treble
Middle
Bass
Reverb
Speaker(s) 2 x 12" Celestion G12M, 2 x 10" 7442 Celestions
Size (Head) 24" W x 10" H x 11.25" D
Size (cabinet size, less hardware) 34" W x 26" H x 11.75" D
Accessories Covers, foot pedal and trolley

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© 1998 - 2017 The Vox Showroom, all rights reserved. No use on online auctions, eBay or Reverb.
Jennings Musical Instruments, the UK manufacturer of Vox, decided to refresh their amp line by introducing a new series of guitar and bass amplifiers in 1966. Known as the UL Series, with "400 Series" models for bass and "700 Series" models for guitar, these new amps were intended to replace the "AC" series lineup that had propelled Vox gear to the top of the pops.

The two smallest models of the UL Series, the 705 and 710, were all tube designs, derivatives of their predecessors, the AC-4 and AC-10SRT. Vox completed the UL Series with new 15, 30, 60 and 120 watt RMS hybrid designs that featured a modular solid state preamp with a tube output stage. The modular design concept and much of the circuitry of these unique new British Vox amps was actually inspired by developmental work completed at the Thomas Vox Labs in Sepulveda California.

History and Development of the UL Series
Vox products arrived on the American shores in late 1964 after a two-sided distribution contract was inked between Jennings Musical Instruments in the UK and Thomas Organ of Sepulveda, California. Thomas Organ imported JMI products as the sole US distributor of Vox while JMI imported console organs as the sole UK distributor of Thomas Organ products.

In less than a year, Thomas Organ renegotiated the terms of the Vox distribution agreement for the US. Due to the high costs of shipping and customs, Thomas decided it would be more profitable to build their own Vox amps in the US rather than import them from the UK. Thomas also wished to further reduce costs through a complete redesign of the Vox amp line. As a first priority, tube designs would be dropped in favor of transistors. A second priority was the development of a standardized preamp/control section that could be combined with modular power amps of various RMS power outputs to facilitate rapid product development and offer greater economy in production.

Thomas Organ hired a brilliant electronics engineer, Sava Jacobsen, to lead this solid state conversion and standardization project. Jacobsen had recently worked on a similar project for Fender in 1964. His work at Thomas led to the development of a solid state standardized preamp/control section that would find its way into the new US Vox Viscount, Buckingham, Royal Guardsman, Westminster and Super Beatle amplifiers.

In late October, 1965, JMI Vox lead amp engineer Dick Denney traveled from the UK to California to get a first hand look at the progress made toward the conversion from tube to solid state amp circuitry at the Thomas Vox development labs. Denney had the opportunity to audition the solid state replacement for the AC-30, the "Viscount." He also tried out the solid state replacement for the AC-100, the "Super Beatle." As the trip ended, Denney started to recognize the advantages of modular amplifier construction using standardized solid state preamp and power amp sections. The new Thomas Vox amp designs would begin to influence the development of new amplifiers at JMI.

JMI was not yet willing to make the jump to a totally transistorized amplifier due to the reliability issues JMI had with the output stage of the solid state T.60 bass amp. JMI was not confident in the dependability of transistors in the higher current power amp stages of an amp, but felt comfortable using transistors in the preamp section. JMI developed a revolutionary new hybrid amp design that would incorporate a modular solid state preamp section with a tube output amplifier. This solid state preamp/tube output stage hybrid concept would become the basis for the new Vox "UL Series" amp line introduced in 1966.

A 1965 Vox catalog announcing the UL Series stated that "this amplifier was produced to meet certain special electrical and fire safety
regulations enforced in the United States and Scandinavian countries." This would suggest that the "UL Series" name likely refered to the potential for an Underwriters Labratory approval for the amp's circuitry.

Fifteen, thirty, sixty and one hundred twenty watt versions of these hybrid solid state/tube amps would be produced under sub contract to Vox by Triumph Electronics, a UK based amplifier manufacturer. At first JMI expected to replace all of the "AC Series" amps with these new UL models but the popular demand for the AC-30 and AC-50 models was sufficient to continue their production.

The UL 760 Amp
The preamp section of the UL760 was completely solid state, similar to the modular preamps found in the Viscount and Super Beatle amps Denney had seen at the Thomas Labs in California. The preamp circuitry featured hand wired, point to point construction on tag strips, unlike the printed circuit board construction used on US Vox amps. The same modular preamp circuitry used in the UL 760 was also incorporated into the UL 715 (15 watt), UL 730 (30 watt) and UL 7120 (120 watt) amps.

The UL 760 was a two channel amp. The first, or "Vibrato" channel, had volume, treble, middle, bass, vibrato speed and vibrato depth controls plus a "Boost" switch. The Vibrato channel also had a foot switchable distortion or "fuzz" circuit. The "Normal" channel had volume, treble, middle and bass controls plus a "Boost" switch and reverb.

A single reverb control in the UL 760 introduced reverb to the Normal channel and used the infamous Vox crystal phono cartridge reverb pan.

The reverb pan designed by JMI for the UL 760 used a single delay spring between two 1 volt output Sonotone 2T crystal phono cartridges. These cartridges were used as the reverb drive and receive transducers.

Tom Jennings, the president of JMI Vox, resented having to pay the $1 per amp licensing fee charged by Hammond Accutronics fee for the use of their patented reverb pan. The Vox crystal phono cartridge reverb pan just barely skirted the patents on the Accutronics unit.

About all one could say about the JMI reverb pan is it worked to a degree, but the tone and depth of the reverb was certainly lacking when compared to Fender amps of this era. Furthermore, this phono cartridge based reverb pan would easily slip into a howling acoustic feedback if the amp was played too loudly.

A three button foot switch allowed remote actuation of the reverb, tremolo and distortion features in the UL 760.

A formed full face anodized aluminum front panel was illuminated by a series of small lamps, located just above the diamonds in the front panel (see picture at left).

The head cabinet for the UL 760 (and UL 7120) was slightly larger than the head cabinets used on the UL 715 and UL 730. The cabinets were constructed of lock jointed 13 ply baltic birch plywood and were covered in traditional Vox black basket weave vinyl. The UL series marked the first use by Vox of "two pin" corners and the partial elimination of the rounded wooden cove used in the inside corners of the cabinet. This change was made necessary as the lip of the "one pin" corners would have obstructed the removal of the chassis through the front of the cabinet. Eight Vox logo air vents are mounted to the top of the amp, three are on the bottom. Two Vox logo handles are mounted on each of the ends of the top of the head cabinet. Wooden support rails replaced the feet (see photo at left).

The power amp section of the UL 760 included two KT-88 and one ECC83 tubes. Individual bias controls for the output tubes are visible through the rear panel of the head cabinet. The removable power cord used a four conductor XLR connector on the chassis end. A rear panel mounted five position rotary voltage selector allowed the UL 760 to be adjusted for the mains voltage in any country. Twin speaker out jacks were provided along with an 8 - 16 ohm speaker selector switch.

The open backed UL 760 speaker cabinet featured two 12" Celestion G12M (now known as "Greenback") speakers and two Celestion 15 watt 10" speakers. The trapezoidally shaped injection molded plastic Vox logo had white letters, a departure from the gold letters normally found on Vox amp logos. Like the heads, the speaker cabinets were also constructed of 13 ply baltic birch plywood and were covered in traditional Vox black basket weave vinyl. Black Vox diamond grill was standard.

A chrome plated tubular roller trolley included swivel mounts and Vox logo hand wheels.

In 1991, Dick Denney co-authored a book on the history of Vox called "The Vox Story." Denney reported on page 61 of his book that "although the (UL 700 and UL 400) amps were loud and reliable, they had a bland and unremarkable sound which failed to engage the interest of most of the top groups it had been undoubtedly aimed at." Failing to achieve significant sales numbers in the UK, the large majority of hybrid UL amps were sold by Vox distributors on the European continent.

In 1967, Jennings Musical Instruments introduced a series of new modular amps that were totally solid state. These new models replaced the UL Series. Dick Denney told me that many, if not most of the hybrid UL amplifiers produced by Vox and sold in the UK were traded back to Vox by customers a year later in exchange for these new all solid state amps. He also told me that JMI destroyed the Vox UL amps that were traded back.

No mention of the UL700 or UL400 Series amps is made in the 1967 UK Vox catalog.

Price
The JMI 1966 price list addenda indicated that the UL760 head and matching speaker cabinet retailed for £210. By comparison, an AC-50 Super Twin head and cabinet retailed for £184 in 1966.





North Coast Music offers many
replacement, repair and restoration
parts for the Vox UL 760
Some are shown below.



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The VOX Showroom!


Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


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