JMI Vox UL 710 Amplifier





Close up view of the illuminated panel lamps




Image from the 1966 Vox catalog from Germany
showing the 710 amp with "Fender" style tilt back legs
By late 1965, JMI Vox in the UK realized that the designs of the "AC Series" amps that had popularized their product line in the first half of the 1960s were starting to show their age. It was time for Vox to have a face lift.

At the same time, Thomas Organ in California was working on new solid state Vox amps designs that they intended to produce for the American market. The US distribution contract inked between JMI and Thomas Organ included a provision that allowed Thomas to design and produce their own Vox products in the United States. 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. 

The decision by Thomas Organ that led to the transistorization of the US Vox line had a profound impact on the British side of Vox. Not only did it deny sales of British Vox amps to the burgeoning US market, it also steered JMI away from tube based amp designs and toward the development of solid state circuitry for future products.

Not yet willing to make the jump to a totally transistorized amplifier, lead JMI design engineer Dick Denney developed a revolutionary new hybrid amp design that would incorporate a modular solid state preamp section with a tube output amplifier. This 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 an Underwriters Labratory approval for the amp's circuitry. I have not read any credible support to suggest that the initials "UL" stand for "Ultra Linear" as some have indicated, but I am open to view any evidence to that claim.

Fifteen, thirty, sixty, and one hundred twenty watt versions of these hybrid solid state/tube amps would be produced for both guitar (UL 700 Series) and for bass (UL 400 Series). JMI expected to replace the "AC Series" amps with these new UL models.

Vox would also need several lower wattage models to round out the UL line. The all tube, hand wired Vox UL705 would replace the aging Vox AC-4. The all tube, hand wired Vox UL710 would replace the Vox AC10SRT.

Like its bigger UL Series brothers, the UL710 featured a formed anodized aluminum front panel. A series of five small lamps, located just above the diamonds in the front panel, illuminated the controls. The single channel, dual imput amp had controls for volume, bass, middle, treble, tremolo speed, tremolo depth and reverb. A "Boost" switch increased the gain of the preamp.

The UL710 had three ECC83 (12AX7) preamp tubes, two EL-84 output tubes, and an EZ81 tube rectifier.

A rear panel mounted five position rotary voltage selector allowed the UL710 to be adjusted for the mains voltage in any country.

The UL710 carried over the infamous Vox crystal phono cartridge based reverb pan used in the AC10SRT.

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. Instead, he designed his own reverb pan, just barely skirting the patents on the Accutronics unit.

The reverb pan designed by JMI used two 1 volt output ACOS GR71 or two Sonotone 2T crystal phono cartridges for drive and receive transducers. A single delay spring was connected to the needle saddles of each cartridge.

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.

The open backed speaker cabinet designed for the UL710 had two 10" Celestion speakers. Some of the UL710 speaker enclosures came from the factory with adjustable swivel side stands. Yet another version of the UL705 speaker cabinet included a set of "Fender" style chrome plated tilt back legs. A black and white image of these tilt back legs is shown at left from the 1966 Vox German catalog.

The UL710 speaker cabinet featured a trapezoidally shaped injection molded plastic Vox logo with white letters. This was a departure from the gold letters used on Vox amp logos previously.

Price
The JMI 1966 price list addenda indicated that the UL710 head and matching speaker cabinet retailed for £100. By comparison, an AC-10 Twin retailed for £60 in 1966.

While a great sounding amp for its size, the UL710 was expensive and not well received in the UK. It appears that a large majority of the UL710 production was sold by Vox distributors on the European continent.



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