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UK VOX AMPS History of Vox in the UK JMI Era Vox Amps: 1959-65 JMI Era UL Series Hybrid Amps: 1966-67 JMI-VSL Era Solid State Amps: 1967-73 VSEL/Corinthian Era Vox Tube Amps: 1968-70 Birch Stolec Era Vox Amps: 1970-73 Dallas Era Vox Amps: 1973-78 Rose Morris Era Vox Amps: 1978-92 Korg Era Tube Amps 1993-25 Korg Era Solid State and Hybrid Vox Amps:1999-25 Korg Era Vox Valvetronix Amps - 2001-16 US VOX AMPS VOX ORGANS VOX GUITARS Vox Solid Body Elec Guitars: 1960-88 Vox Semi-Acoustic Elecric Gtrs: 1964-68 Vox Acoustic Guitars: 1964-70 Vox Bass Guitars: 1962-87 Voxton Guitars & Basses: 1969-70 Vox Gtrs & Basses, Korg Era: 1998-25 VOX FX & MISC View All Products Vox Tape Echo & Reverb Units:1963-68 Vox Microphones and Mixers Vox Boosters Vox Wah Wah Pedals: 1967-2025 Vox Effects Pedals: 1965-2025 Vox Tonelab & Stomplab FX Processors Vox Amplugs Vox Ampliphonic Accessories: 1968 Vox Accessories Vox Promotional Items VOX CATALOGS VOX MANUALS MY VOX BAND SEARCH WHAT'S NEW

The Vox Solid State Escort 50 Bass Amplifier - A Look "Under the Hood"

Cabinet In contrast to the premium finger-jointed, 13-ply Baltic birch cabinets manufactured by Vox in the 1960s, the Escort 50 Bass enclosure used simpler butt-jointed particle board reinforced internally with heavy wooden cleats. Chassis The Escort 50 Bass featured an inverted "L" shaped, 16-gauge steel chassis that anchored most of its circuitry. Beyond mounting the electronic components, the chassis also functioned as a heat sink for the output transistors. The power transformer was the only electronic component not mounted to the chassis; instead, it was secured directly to the bottom of the cabinet. Circuit Board A single phenolic printed circuit board housed the preamp circuit, tone controls, power amp drivers, and power supply (minus the mains transformer). This board was secured to the chassis by the five PC mount potentiometers. Screws on each end of the chassis fastened it to the amplifier cabinet. Single Rail Power Supply Configured for worldwide use, the Escort 50 Bass relied on a power (mains) transformer with a tapped primary winding to accommodate multi-voltage operation at 115, 220, or 240 VAC. Its single, untapped secondary winding fed an IN5404 diode bridge rectifier in conjunction with a 1000 µF smoothing capacitor to generate a +80 VDC rail to supply the power amplifier circuit. This +80 VDC rail voltage was then stepped down to +30 VDC to power the preamp stage via a 1k 5W resistor and a 30V Zener diode. The Escort 50 Bass had a 1.6AT (slow-blow) fuse located on the control panel. 50 Watt Quasi-Complementary Power Amplifier Circuit The Escort 50 Bass employed a quasi-complementary power amplifier circuit using two 2N3055 NPN output transistors to emulate a standard NPN-PNP push-pull pair. It accomplished this by using a traditional Darlington pair (BD537 NPN driver transistor + 2N3055 NPN output transistor) for the upper half of the wave and a Sziklai pair (BD538 PNP driver transistor + 2N3055 NPN output transistor) for the lower half of the wave. This Sziklai pair configuration effectively simulated a high-power PNP output transistor, bypassing the high costs and reliability issues associated with early PNP power transistors. The audio signal from the output transistors then passed through a 1000uf electrolytic capacitor before reaching the speakers. This capacitor was critical to isolate the amplifier's DC biasing voltages from the speaker output. Without this capacitor acting as a barrier, the DC biasing voltage from the 2N3055 output transistors would instantly burn out the speaker's voice coil. Preamp Circuit The entire preamp circuit, including the tone controls, was powered by a single RC4136 quad opamp. The RC4136 included four independent amplification circuits in a compact 14-pin DIP (dual in-line) package. The RC4136 significantly streamlined the layout of the circuit board and completely eliminated the need for discrete transistors in the preamp circuit. Schematic Download the factory schematic for the Escort 50 Bass by clicking here.