JMI Vox AC-50 "Mk I" Four Input Single Channel Amplifier Head - 1964
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This was the second version of the Vox AC-50 head. It combined the quad input single channel copper control panel AC-50 chassis with the Mk I "small box, thin edge" cabinet. It was produced in 1964.

The original version of the AC-50 was a single channel amplifier with dual 1/4" instrument inputs. The copper control panel featured volume, treble and bass controls, indicator lamp, power switch, fuse and a plug style voltage selector. The tube complement included a GZ34 tube rectfier, two fixed biased EL34 power tubes, two ECC83 (12AX7) and one ECC82 (12AU7) preamp tubes.

The second version of the single channel Mk I chassis (shown above and at left) was identical to the first except it had four 1/4" instrument inputs rather than two. These were arranged into the shape of a diamond on the left side of the control panel.

Lead JMI Vox engineer, Dick Denney, once told me that Vox tried to make their amp heads no larger than the size of a "lunch pail" whenever possible. This "small is better" influence was certainly at work in the case of the "small box, thin edge" AC-50 heads. The cabinet was designed to be no larger than necessary to enclose the chassis.

The cabinet was constructed of 3/8" baltic birch throughout. The cabinet had a Vox logo handle, a small Vox logo, pancake feet, and two expanded aluminum vent grills. Additional venting was provided in the front grill cloth panel. No corners were supplied because the corners normally used on Vox cabinets were incompatible with the "thin edge" cabinet construction.

The chassis was fastened to the bottom of the enclosure with machine screws. This model predates the use of a chassis slider board on the AC-50. Chassis slider boards were introduced on the Mark III version of the AC-50.

Three XLR jacks were mounted on the rear panel. The two three pin XLR jacks on left were for speaker output. The right, four pin XLR jack was used to supply AC mains voltage to the amplifier.


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