Vox v251 guitar organ service manual

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Brand: Vox

Model V25 1

Product: Guitar Organ
Description: Service Manual

Musicparts Document Number: 52058 TechTips: No Pages: 19 Dated: 1966-67

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GUITAR ORGAN

GUITAR

V251

SERVICE INFORMATION

Thom-s Org-n Company O Nation! Sank. Department 0 sopulvodc, Haml-

OIRCUIT DESCRIPTION

MASTERBOARD

The Masterboard is the main electronic assembly of the Guitar Organ. It consists of
the following:

A. Voltage Regulator {Stabilizer}

This unit is located on the Masterboard adjacent to the voicing filters. Its schematic
is shown on drawmg No. 05/091. The stabilizer is set to deliver a constant 8.4 volts D. C.
to the Percussion Circuit by adjusting V33 (250 Ohm Potentiometer).

B. 'l'one Generator & Divider Boards

There are 6 Tone Generators, one to mash each of the guitar strings. The master
oscillator is an emitter coupled multivibrator consisting of transistors TR]. and TR: plus
their associated resistors and capacitors. (See Drg. No. 05/068).

The frequency of oscillation is determined by the tuning capacitor Cl and the total
neck resistance between pin 8 of the Tone Generator Board and ground. When the open
button for any of the string tones is depressed. all of the series neck resistors are in the
circuit. This produces the lowest frequency. The tuning control VRi (for the associated
Tone Generator) on the Master-board is used tor fine tuning. When the l2th fret is played the
octave tuning control VR2 (for the associated Tone Generator) on the Masterbcard is used
to tune the octave. When V32 is adjusted, it may be necessary to retune VRl.

Transistors TR3 and T84 plus their associated components form a bi-stable Eccles-
Jordon frequency divider. There are two divider outputs taken from the collector of TRi:

(1) A Sigial is fed from the collector of TR4 througi resistor 316 and capacitor
CS to pin 3 of the T.G. Board. From pin 3, this signal is fed to the octave switch, and then
to the effects switch.

(2) Another signal is taken from the collector oi . . and fed through the flute
filter comprised of resistors R17. R18, R19 and capacitors C7. t. , and 010.

The output of the flute filter is connected to pin 2 of the 'l. G. Board. This signal from pin

2 is ted to the flute switch. and then to the output of the effects switch. The combination

of tones either go through or bypass the percussion unit depending upon whether "percussion"
is swnchgfon or oil.

38-5431-0 Printed in U.S.A. ~oril 1967