Amp_Scrapbook 电路图 维修原理图.pdf

This workbench gadget allows you to connect a light bulb in SERIES with your amp. It will allow you to determine if your amp is drawing excessive current due to a shorted PT or filter caps, etc., without blowing fuses or smoking valuable components such as a PT. A dead short on the primary side of the PT will cause the bulb to glow at full brightness. Partial shorts or a short on the secondary side of the PT will show some increased level of brightness. A properly working amp will cause the bulb to glow fairly bright when first turned on, but will fade to a dimmer glow as the amp warms up. The fancy version above includes a pushbutton switch that bypasses the outlet allowing you to see the lamp at full brightness. Once you have confidence that there is no high current drain from your amp, you should remove this gadget. Voltage measurements will be very low and probably meaningless while your amp is plugged into this gadget. 60100 Watt Bare Bones Current Limiter 收音机爱好者资料库 Ra d i o Fa n s .CN Buckaroo! AC adapter for old amps NEUTRAL LINE 12.6V UP = 6 volts down CENTER = OFF DOWN = 12 volts down Radio Shack Cat # 273-1511 12.6 VAC 3 A With center tap This gadget uses a “bucking” transformer to reduce AC line voltage. Its useful for reducing todays 120-125 VAC line voltage by approximately 6 or 12 volts which will also reduce your HT and filament voltages by an equal percentage. (Tip. If you find that the output voltage actually increases, you have the transformer phased for a “boost” operation. Simply reverse the primary leads to correct this.) Note. I actually used a 4PDT switch just because I had one. 6.3V DPDT center off 收音机爱好者资料库 Ra d i o Fa n s .CN To Bias Cathode/Fixed Bias Switch B 470 470 Pentode/Triode Switch A Marshall 18 Watt Power Dampening Switch (can be adapted to other LTP phase inverters) 47K 470K 56K 22K 15K 10K 4.7K 470K 820 LTP PHASE INVERTER 330 100K 330 100K Bias resistor Bypass cap Power tube #1 cathode Power tube #2 cathode Bypass cap Bias resistor Da Geezers Bypass Cap attenuator (Bias resistor value will be 2X the value of a single bias resistor) UP = full power Center to power Down power (power estimates based on using 330) DPDT /w Center OFF + + 25F 25V + + 25F 25V 收音机爱好者资料库 Ra d i o Fa n s .CN Guitar Amp Return Send 9v +- tip ring Stereo Jack Switchcraft #12B Standard Jacks Switchcraft #11 3PDT push/push RX 9 - VLED ILED RX= G T R GT GT GT Return Amp Guitar Send 9 V +- K 3PDT Switch operation is up/down 1500 220K 220K 1500 5 8 3 4 8 5 3 4 470 + + 10K 27K BIAS Current flows through bias supply divider network to develop adjustable bias voltage No dc current flows through grid or grid resistors, therefore no dc voltage is dropped across grid resistors Where does the current flow? 47K Bias Range B+ Bias voltage 15K 56K Class X .047F Bias circuit and full wave bridge from Marshall JCM900 and some old Ampegs (See following page for circuit description) BIAS Range Separate bias winding and full wave bridge (nice when you have a separate bias winding) 470 + 10K 27K Typical Fender AB763 from bias tap 220K Bias Deluxe/Deluxe Reberb use 10K Additional failsafe resistor 220K + 47K 25K Typical Marshall from HT winding Bias + 15K 50K 10F10F 340VACppwith 0V baseline Notice that this waveform never goes negative with respect to ground. If you were to apply this signal directly to the cathode of this simple half wave rectifier, the diode would block the entire waveform and the resulting DC output would be zero volts. 222VACpp(170V positive, 52V negative) Well, C1 and R1 have certainly affected the shape and amplitude of the input AC waveform. But more important, the baseline has shifted and now a portion of the signal goes below zero volts. The diode blocks the positive portion and passes the negative portion. The resulting unloaded DC output is now -52VDC. How does it work? The test bias circuit inside the blue circle was just breadboarded and connected via clip leads to the power supply of my Revibe. The AC at the bridge is a pulsing positive DC waveform. C1/R1 couple this waveform to the input of the diode and also shift the baseline such that the waveform now has a positive as well as negative half cycle. Shifting the baseline in this manner is the key to the operation of this bias circuit. +170V -52V 0V +340V 0V 100F 125C3A 4.7K/3W10K/3W 258V303V329V NEUTRAL LINE 1 AMP SLO BLO POWER Weber WRVBPT 260VAC 100mA 120Vac 100F100F100F 56K .047F C1 R1 -52VDC (Measured with Fluke 87V) 100 K 25F Bias circuit and full wave bridge (from Marshall JCM900 and some old Ampegs) F = 60Hz To Bias BIAS MODE Cathode Fixed To Bias 1 BIAS BIAS COM 1 BIAS MODE CathodeFixed Figure 1. Use this DPDT switch with any bias supply. Figure 2. Use this SPDT switch with a bias supply that gets its AC supply from one end of the PT HT winding *AND* uses a high value resistor between the PT and the bias rectifier/filter circuit. (See Fender Princeton Reverb for example.) Hi/Lo Input jack switching is often misunderstood. The operation is usually straightforward, but the actual circuit drawing is often confusing, especially to the casual observer. Hopefully the following illustrations will demystify the circuit operation. These first two circuits represent the typical Hi/Lo jacks found in most Fender and Marshall amps. Many other amp manufacturers use this circuit as well. The following circuits represent special case switching. The first shows the Marshall 18 Watt parallel tube switching circuit and the other shows a Marshall JCM-800 high gain cascade switching circuit. 68K 68K 1M HI LO The LO jack delivers the signal to a 2:1 voltage divider made up of the two 68K resistors. The 1meg is shorted out by the switch contacts on the HI jack. The signal taps off the junction of the two 68Ks. Half the signal is dropped across each 68K, therefore only 50% of the signal is applied to the tube. Switch open Switch closed Using the Lo Input 68K 68K 1M HI LO Switch closed Switch open The HI jack delivers ALL the signal to the tube. The signal enters the HI jack and first sees a 1 Meg resistor to ground. Since the LO jack switch is closed, the two 68Ks are parallel for an effective resistance of 34K and the signal travels through the paralleled 68Ks to the tube. There is no voltage divider so 100% of the signal arrives at the tube. Using the Hi Input VOL LO HI Marshall JCM-800 2204 Channel Inputs The LO jack delivers the signal directly to V1B for a single gain stage. The HI jack delivers the signal to V1A and then to V1B through the closed switch of the LO jack. The cascaded tubes give a high gain sound. V1AV1B LO 1M 1M HI Marshall 18 Watt Normal Channel Inputs The LO jack delivers the signal to V1A only. The HI jack delivers the signal directly to V1B and also to V1A through the closed switch of the LO jack. The parallel tubes give a fatter sound with a slight gain increase. V1BV1A 68K 68K 1M J2 HI J1 LO Switch closed Switch open The HI jack delivers almost ALL the signal to the tube. The signal enters the HI jack and is applied to a voltage divider consisting of both 68Ks and a 1M through the closed switch on J1. 6% of the signal is dropped (lost) across the first 68K. The other 94% signal that is dropped across the second 68K and 1M is applied to the tube. Type BUsing the HI input 68K 68K 1M J2 LO J1 HI Switch open Switch closed The HI jack delivers ALL the signal to the tube. The signal enters the HI jack and first sees a 1 Meg resistor to ground. Since the LO jack switch is closed, the two 68Ks are parallel for an effective resistance of 34K and the signal travels through the paralleled 68Ks to the tube. There is no voltage divider so 100% of the signal is applied to the tube. Type AUsing the HI input 68K 68K 1M J2 LO J1 HI Switch closed Switch open The LO jack delivers the signal to a 2:1 voltage divider made up of the two 68K resistors. The 1meg is shorted out by the switch contacts on the HI jack. The signal taps off the junction of the two 68Ks. Half the signal is dropped across each 68K, therefore only 50% (-6db) of the signal is applied to the tube. Type AUsing the Lo input 68K 68K 1M J2 HI J1 LO Switch open Switch closed The LO jack delivers the signal to a 2:1 voltage divider made up of the two 68K resistors. The 1meg is removed from the circuit by the switch contacts on the HI jack. The signal taps off the junction of the two 68Ks. Half the signal is dropped across each 68K, therefore only 50% (-6db) of the signal is applied to the tube. Type BUsing the Lo input There are two variations of the input switching jacks for this amp. Type A is the classic circuit that has been used in many Fender and Marshall amps. Type B uses a slightly different circuit to accomplish the same functionality. The Hi input operation is slightly different for the two type circuits. However, the difference is so slight that it can be practically ignored. You would need precision lab equipment to even measure the slightly different signal levels applied to the tube grid. When comparing the Lo input operation, it can be seen that the two type circuits become identical, although achieved through a slightly different approach. Hopefully, the summary below will explain the functionality of both types and also point out the slight differences. 5 VAC 6 8 2 4 SS/Tube Rectifier Switching Using a SPDT Center Off switch allows for SS STBY TUBE function. 5 VAC 6 8 2 4 This full wave bridge circuit retains the characteristics of a tube rectifier. Note there is no center tap on the HT winding. Hybrid SS/Tube Bridge Full Wave Rectifier V3A - Trem Oscillator V3B Trem Phase Inverter V4A - Low Pass Modulator This unique tremolo circuit is found in several of the old Fender 6G_ amplifiers and also in the Revibe units available from Hoffman or Weber. The sound is much richer than other typical tremolo circuits. The Oscillator V3A is a standard Phase Shift Oscillator that operates at a low frequency range of approximately 2-10 Hz. The oscillator output is applied to the grid of V4A through the Intensity control. The tremolo signal from the Intensity control is also sent to the grid of phase inverter/amplifier V3B. The 180 out of phase tremolo signal is applied to the grid of V4B. These two tremolo signals will control the gain of the modulator tubes by varying the bias at the slow oscillator frequency. The input guitar signal is split and also applied to the grids of the modulator tubes. However, the guitar signal passes through a low pass filter (blue path) to get to V4A and passes through a high pass filter (green path) to get to V4B. So, the V4A amplifies only the low frequency components of the guitar signal and the gain is varied/modulated by the Tremolo oscillator signal. Likewise, V4B amplifies only the high frequency components of the guitar signal and the gain is varied/modulated by the Tremolo oscillator signal that is 180 out of phase with the Tremolo signal applied to V4A. The modulated high frequency guitar signal is recombined with the low frequency guitar signal in the two 470K mixing resistors. The out of phase Tremolo signals are also recombined in these mixing resistors, but since they are equal amplitude and 180 out of phase, the Tremolo signals cancel each other, leaving only the guitar signal. Since the Tremolo signals cancel each other, you will not hear the Tremolo signal breathing when no guitar signal ia applied. Guitar Input Guitar Output V4B - Hi Pass Modulator Trem Oscillator/DriverPhase SplitterModulator The Oscillator is a standard Phase Shift Oscillator that operates at a low frequency range of approximately 3-10 Hz. The oscillator output is coupled through a cathode follower driver and then applied to the input of a phase splitter through the Intensity control. The phase splitter produces two identical outputs that are 180 out of phase with respect to each other. Each output is coupled to the grid of a modulator tube and will control the gain of that tube by modulating the bias at the slow oscillator frequency. The input guitar signal is split and also applied to the grids of the modulator tubes. However, the guitar signal passes through a high pass filter to get to the top tube and passes through a low pass filter to get to the bottom tube. So, the top tube amplifies only the high frequency components of the guitar signal and the gain is varied/modulated by the Tremolo oscillator signal. Likewise, the bottom tube amplifies only the low frequency components of the guitar signal and the gain is varied/ modulated by the Tremolo oscillator signal that is 180 out of phase with the top Tremolo signal. The modulated high frequency guitar signal is recombined with the low frequency guitar signal in the two 470K mixing resistors. The out of phase Tremolo signals are also recombined in these mixing resistors, but since they are equal amplitude and 180 out of phase, the Tremolo signals cancel each other, leaving only the guitar signal. Since the Tremolo signals cancel each other, you will not hear the Tremolo signal breathing when no guitar signal ia applied. Guitar Output Guitar Input Low pass High pass This circuit is also found in several other 6Gxx amplifiers AMP 8 OHM SPEAKER CAB #1 4 OHM SPEAKER CAB #2 4 OHM Special Y cable used to connect an amplifiers 8 output to two 4 speaker cabs. This Y cable connects the speaker cabs in series providing the correct load match for the amp. Connect RED wires to plug tips. Make this splice connection inside the plug shell Typical Fender Mains Wiring FUSE AC CORD Com NEUTRAL LINE Class X .047F 630v to PT Primary Improved Fender Mains Wiring FUSE AC CORD Com NEUTRAL LINE Class X .047F 630v to PT Primary Improved Fender Mains Wiring with switched outlet