Fender 63 reverb manual
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Page 1
63 Fender Reverb (This is the model name for warranty claims) SERVICE MANUAL JUNE 1994 REV A TYPE PR 263 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
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63 Fender Reverb THEORY OF OPERATION The input jack contains a Tip Shunt switch contact which will ground the input when the plug is removed. The input impedance consists of R1R11 and R12 in parallel, and equals approx. 500k ohm. The first stage (V1A) provides a voltage gain of 38.8 (V out/V in = 1.94V/50mV =38.8). Bypass capacitor C2 increases the AC gain, and also reduces hum. The voltage divider R2 and R3 reduce the voltage so the overall gain is about 3. The signal then feeds the Dwell control, which determines the amount of signal sent to the reverb drive circuit. V1B provides a voltage gain of 20. C3 and R9 make up a single pole filter which provides 6db per octave of low frequency roll off at 300Hz. Excessive low frequencies can make the reverb sound unnatural and boomy. V2 is a 6V6GT power tube which supplies voltage and current gain to drive the reverb transformer. Due to the lack of availability, the original 6K6 power tube was replaced with a modern 6V6. CR7 (56V Zener) protects C4 from exploding if V2 develops an internal short. This is necessary to conform to modern day NEMKO safety requirements. The footswitch turns the reverb on and off by grounding the input to the reverb recovery circuit. R13 provides a ground reference (or bias) for the input of V3A. This prevents instability in V3A if the reverb recovery cable is disconnected from the reverb pan. V3A senses the reverb return signal and amplifies it with a gain of about 37. The Tone control (R17) attenuates the high frequencies above 3kHz, through C9. C10 provides a slight bass roll off which is affected by the position of the Mix control in relation to the input impedance of the guitar amplifier. V3B is a cathode follower, unity gain buffer amplifier for the dry signal. C11 is a non-polarized, metalized polyester film capacitor, which is located across the high voltage transformer secondary, suppresses EMI frequencies from 20kHz to 30mHz. This is necessary to conform to modern day NEMKO safety requirements. The pot mounting brackets are all connected together via traces on the circuit board. The trace connects to the star audio ground through R22, R22 places 15 ohms of resistance between audio ground and the pot mounting brackets. This is done for two reasons. Fist, with the circuit board installed, the pot brackets are physically connected to chassis/earth ground. R22 isolates audio ground from earth ground through the pot brackets. This eliminates internal ground loops. Secondly, when the circuit board is removed for repair and testing, R22 provides a ground reference (15 ohms) for the pot brackets. R23 places 15 ohms of resistance between audio ground and chassis/earth ground. This minimizes hum by eliminating ground loops internally and externally when connection with other units. R22 and R23 are Flame Proof/Fusible resistors. If excessive current flows through theses resistors, they will not burn, they will simply open. CR5 & 6 (across R23) provide an important safety feature. IF the guitar amp chassis becomes electrified, current will flow through the coax cable to the power supply ground of the Fender Reverb unit. The current will seek earth ground through R23. When R23 opens, the earth ground connection is broken. This will electrify the reverb units ground and thus the guitar (ouch!). CR5 & 6 provide an alternate path to earth ground if R23 opens.