Fender vibro king manual
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Page 1
VIBRO-KING (This is the model name for warranty claims) SERVICE MANUAL JUNE 1994 REV A TYPE CSR 4 IMPORTANT NOTICE: The information contained herein is CONFIDENTIAL and PROPRIETARY to Fender Musical Instruments Corp. It is disclosed solely for use by qualified technicians for purposes of equipment maintenance and service. It is not to be disclosed to others without the expressed permission of Fender Musical Instruments Co. All specifications subject to change without notice. For warranty repair service, only Fender specified part numbers are to be used. It is recommended they also be used for post-warranty maintenance and repair. Parts marked with an asterisk ( *) indicate the required use of that specific part. This is necessary for RELIABILITY and SAFETY requirements. DO NOT USE A SUBSTITUTE! A coded naming convention is used in the description of certain parts. The codes and what they mean are as follows: CAPACITOR CODES HARDWARE CODES CAP AE = Aluminum Electrolytic BLX = Black Oxide CAP CA = Ceramic Axial CR = Chrome Plated CAP CD = Ceramic Disk HWH = Hex Washer Head CAP MPF = Metalized Polyester Film M = Machine Screw CAP MY = Mylar NI = Nickel Plated CAP PFF = Polyester Film/Foil OHP = Oval Head Phillips PB = Particle Board RESISTOR CODES PHP = Pan Head Phillips PHPS = Pan Head Phillips Sems RES CC = Carbon Comp SMA = Sheet Metal "A" Point RES CF = Carbon Film SMB = Sheet Metal "B" Point RES FP = Flame Proof SS = Stainless Steel RES MF = Metal Film TF = Thread Forming RES WW = Wire Wound ZI = Zinc Plated
Page 2
VIBRO-KING THEORY OF OPERATION J1 and J2 are summed by R11 and R12. These 10K Ω resistors are a lower than usual value for a tube amplifier. This value was chosen for two reasons. 10K Ω is smaller than 33K Ω or 68K, Ω therefore the amplifier will produce less noise at high volume settings. Secondly, when linking two or more amplifiers a common trick is to plug the guitar into Input 1 and use Input 2 as the output to the next amplifier. With 68K Ω resistors, 1/10 th of the signal is lost with each link. After the input resistors, the signal is split and fed to V1A and V2A. V1A serves as a preamp for the Reverb Drive, or Dwell control. The Dwell control feeds V3, a small power tube which drives the Reverb. V2A is a Cathode-Follower circuit which creates a low impedance, isolated (from the input) signal to drive the Mix control (R2). V2B amplifies the Reverb return (sense) signal and sends it to the Tone control (R3). High frequencies are sent (shunted) to ground via C17. Varying R3 will move the wiper closer to or further from C17, thus making the Reverb brighter (Clockwise) or duller (Counterclockwise). The Reverb signal then sums with the Dry signal at the Mix control (R2). After the Mix control, the signal travels to the Send jack (J3) of the Effects Loop. The signal is then Normaled to the Return jack (J4) and drives V4A. This configuration allows the Reverb functions of the Vibro King to be sent out to other amplifiers (via the Send jack). It also enables a player to insert a delay unit between the reverb and the amplifier for a Rock-A-Billy type effect. A Volume pedal can also be inserted to control the Guitar and the Reverb. The V4A circuit contains the Fat switch (S1). The Fat switch connects C4 to ground to provide a 3dB increase in gain, mostly in the low and mid frequencies. R17 is there to prevent popping of the Fat switch when actuated. NOTE: the Fat switch may pop the first time it is switched. This is due to the warm- up/stabilization cycle of the tube. The Volume control R4A is linked to R4B. R4B reduces the gain of the Reverb at high volume levels. This allows adjustment of the Volume without readjusting the Reverb Mix control. From the Volume control (R4A), the signal is fed to V4B, the Tone control driver section. The signal leaves the tone controls through the Treble control (R5), and is fed to the Vibrato and Phase Inverter circuits. V6B is a low frequency oscillator. The Speed control (R8) varies the oscillation frequency. V6A is the Neon Lamp driver. The lamp flashes faster or slower based on the position of the Speed control (R8). The brightness of the neon bulb is sensed by two LDRs (Light Dependent Resistors) in parallel. The resistors connect to the Intensity control (R9) which varies the amount of attenuation. Because the Vibrato circuit connects to the amplifier directly after the Treble control, the high frequencies will attenuate before the bass frequencies. This simulates a rotating speaker effect. (TROUBLESHOOTING TIP: If the Vibrato does not function, first check the footswitch jack. The switching part of the jack serves to short one side of R57 to ground. If R57 is not grounded, the Vibrato will not operate. If the Vibrato exhibits a clicking sound, the problem is caused by the position of the neon bulb in relation to the LDRs. Adjust the bulb by gently pulling on the leads. Test and repeat as necessary.)