Series 90 V133 Preamp Head: Close Up
1969 - 1971

The V133 Series 90 head was unique as it did not have a power amplifier or internal power supply and was incapable of operation unless connected to either a Series 90 V130 or a V131 powered speaker cabinet. The V133 amp head had two channels and a number of effects as described in detail below.

The amp head was interconnected to the powered speaker cabinet using a cable terminated with an eight pin octal connector. The speaker cabinet not only included the power amplifier, it also supplied operating voltages to the head.

The back of the V133 Series 90 amp head featured black Vox diamond grill cloth and a horizontal Vox logo, similar to the styling of the Vox Supreme, Defiant and Conqueror amps introduced by JMI (UK) Vox in 1967. A wingbolt protruded from the center of the grill, as seen in the rear view of the amp head above and in detail below. This secured the reverb pan against vibration while transporting the amp. If not removed before turning the amp on, the reverb would not function properly.

Dimensions and Weight: 8" H x 22" W x 10.5" D, 22 pounds

Free Schematics for the Vox Series 90 V130 & V133 Control Section
Click here to download the original Thomas Organ schematic for the V133 Vox Series 90 control section courtesy of the Vox Showroom and North Coast Music.

Channel one, or the "Normal" channel, had a volume, treble and bass control along with a "Top Boost" switch. It also had a "Distortion Attack" control. This control varied the amount of the fuzz tone introduced into the guitar signal, not unlike the fuzz circuit on the UK made Vox Supreme, Defiant and Conqueror amps. The fuzz could be actuated either by pulling out the pot or by clicking the distortion button on the foot pedal.

Channel two, or the "Brilliant " channel, also had a volume, treble and bass control. Vox voiced the Brilliant channel with significantly less bass than the Normal channel. This decreased amount of low end response made the Brilliant channel sound more "trebly" than the Normal channel.

This channel also included MRB (Mid Range Boost) and the Repeat Percussion effect. Either could be actuated by pulling the pot or by using the remote five button foot switch.

Unlike the MRB circuit previously used on Vox amps that provided 6 db of mid boost at either 450, 600, or 700 hz, the Series 90 MRB circuit featured a sweepable control. This allowed the mid boost to be set at any frequency between 450 and 750 hz.

Repeat Percussion offered an extreme sort of tremolo effect. Rather than pulsing the volume of the input signal at varying speeds and depths of amplitude as done with tremolo, Repeat Percussion clicked the signal off and on in varying speeds. This effect simulated the strumming of a banjo.

The reverb and tremolo controls were positioned between the controls for the Normal and Brilliant channels. A rotary selector switch allowed the reverb and tremolo circuits to be directed to either the Normal or the Brilliant channel.

The right side of the control panel featured the Output Meter and Meter Range switch, the Standby switch, the "E-tuner," and the Pedal jack.

The "Output Meter" was a whimsical feature. If the needle in the meter reached the "red" range while playing the amp, this would seem to be an indication that the amp was distorting. However, by fliippimg the "Meter Range" switch from "High" to "Low," the sensitivity of the meter was decreased, allowing for lower meter readings.

The "Standby" switch allowed the amp to be left at idle when not in use. It also avoided the "thump" sound in the speakers when the amp was turned on.

The "E Tuner" generated an organ like tone that could be used as a tuning reference for a guitar.

The Pedal jack allowed the five button foot pedal to be connected to the amplifier.

The Vox Series 90 V133 preamp head included this five button foot switch with indicator lamps as an included accessory. The foot switch remotely controlled the Distortion, Reverb, Tremolo, MRB and Repeat Percussion effects. This foot switch was also included with the Vox V1143 Beatle amplifier.

The Vox Series 90 V133 preamp head also included this stamped metal clamp and wing bolt that was used to secure the amp head to the speaker trolley.
Here is a closeup view of the wingbolt used to secure the suspended inner aluminum channel and spring delay line against the inside of reverb pan. This protects the pan against excessive vibration during transport. The wingbolt threads into the rear grill panel, as shown in the second photo above. The reverb pan is mounted to the inside of the grill panel.

A protective carrying cover with a carrying pouch was also included with the amplifier.

North Coast Music offers many officially factory licensed replacement and restoration parts for the Vox V133
Series 90 amp head. Some are shown below.


The VOX Showroom!

Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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