The Impact of Thomas Organ at JMI (1965-66)
The introduction of a series of new British made Vox guitar and bass amps in 1967 demonstrated the influence exerted on JMI by Thomas Organ, the manufacturer of Vox products for North America. JMI now moved away from hand-wired tube amps in favor of modular, solid-state circuits built on printed circuit boards.
When Beatlemania blew the roof off at JMI in 1964, the UK Vox amp line was made up of a series of hand wired tube amps whose circuitry shared little in common. Each model had a unique circuit design that was hand wired on chassis mounted tag strips, a highly inefficient and labor intensive process.
Prior to 1967, JMI had produced only one purely solid-state amplifier design. It was a 30 watt hand wired circuit that was included in two models, the T.60 bass amp
and the LW30 guitar amp
. These amps were prone to frequent failure due to the fragile nature of the germanium power transistors in their output stage. It wasn't until Thomas Organ established a successful record of producing transistorized Vox amps in America that JMI was willing to once again attempt production of solid-state amplifiers.
Thomas Organ was a proponent of the efficiency of solid-state modular amp construction using printed circuit boards. Using this philosophy, Thomas designed a three channel transistorized modular preamp chassis for guitar and a second two channel transistorized modular preamp chassis for bass in the fall of 1965. Thomas Organ also developed 30, 60 and 120 watt modular solid state power amps that would connect interchangeably with either the guitar or bass preamp via a nine pin connector. The 60 and 120 watt modular solid-state amp modules incorporated silicon (rather than germanium) output transistors with large heat sinks, making them both durable and dependable. The Super Beatle
, Royal Guardsman
amplifiers were all constructed using combinations of these preamp and power amp modules. The manufacturing efficiencies demonstrated by Thomas Organ would soon have an impact at JMI.
The Vox "UL Series" Reintroduces Solid-State Preamp Circuits and Incorporates Modular Construction at JMI (1966)
JMI decided to develop a "hybrid" UL Series amp line that combined a solid-state preamp with a tube powered output stage, bridging the gap between tubes and transistors. Much of the design and features of the British UL Series models was inspired by Thomas in America.
The hybrid portion of the JMI Vox "UL Series" included models for guitar and bass. JMI designed a solid state two channel preamp circuit for guitar and a second two channel preamp circuit for bass. These preamp circuits were combined with a 15 watt, 30 watt, 60 watt or 120 watt tube power amp to create four guitar amps (UL 715
, UL 730
, UL 760
, and UL 7120
) and three bass amps (UL 430
, UL 460
and UL 4120
While being conceptually similar to the modular US Vox amps, the UL models were quite different in construction. The UL amps were not totally modular as the preamp and power amp circuits were assembled on one chassis. The UL amps featured point to point, hand wired construction while Thomas amps were built on printed circuit boards. The UL amps were "hybrids," having a solid state preamp and tube power amp. The comparable US Vox amps were 100% solid state.
The UL amps were the stepping stones between the all tube amplifiers JMI produced through 1965 and the modular, solid state designs Vox introduced in 1967. As such, the UL amps were only offered in the UK in 1966 while JMI quietly developed their new purely solid state models.
The Arrival of Modular Solid State Amp Design at JMI - 1967