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20 W Stereo Integrated Audio Amplifier

PWB Design

The 20 W Stereo Integrated Amplifier is comprised of three major PWB groups, specifically:

•

The amplifier module, which includes amplifier board #1 (right), amplifier board #2 (left),

the B+ rectifier board, and a pair of speaker terminal boards.

•

The transistorized preamplifier module, which includes a main board and daughter board.

•

The power management module, which is a single board.

Each of these modules are described in the following sections.

3.1

20 W Stereo Amplifier Module

A printed wiring board (PWB) implementation is used that incorporates all components of the

stereo amplifier, except for the transformers, which are mounted on the chassis. The amplifier

module includes amplifier board #1 (right), amplifier board #2 (left), the B+ rectifier board, and a

pair of speaker terminal boards. Each is described in the following sections.

Summary of Contents for JC Whitaker 20 W Stereo Integrated Audio Amplifier

Page 1: ...20 W Stereo Integrated Amplifier WhitakerAudio 20 W Stereo Integrated Audio Amplifier ...

Page 2: ...WhitakerAudio Specifications subject to change without notice Any trademarks used in the manual are the property of their respective owners Note This document is intended to assist readers in building an audio product for personal use See the Warranty for service limits Always use good engineering practices and appropriate safety precautions ...

Page 3: ...sembly of the Transistorized Stereo Preamplifier Module 74 5 4 Assembly of the Power Management Module 80 5 5 Chassis and Final Assembly 85 5 5 1Front Panel Components 85 5 5 2Back Panel Components 90 5 5 3Cable Clamps and Related Hardware 91 5 5 4Install Printed Wiring Boards 93 5 5 5Install Transformers 95 5 5 6Install Remaining Chassis Components 97 5 5 7Wire the Transformer Leads 98 5 5 7 1 Ca...

Page 4: ...raph Preamplifier Measurements 160 7 1 2 1 RIAA Equalization 160 7 2 Power Amplifier Performance Measurement 162 7 2 1IMD Measurement 164 7 2 2Hum Balance Adjustment 164 7 2 3Clipping Point 165 7 2 4Crosstalk 166 7 2 5Square Wave Performance 166 7 2 6Bias Adjustment 168 7 3 Reference Measurements 171 7 4 Thermal Considerations 171 7 5 Final Touches 172 7 6 Baseline Performance Measurements 173 7 6...

Page 5: ...e series of products This amplifier shares the craftsmanship and impressive industrial design of the other offerings in the WhitakerAudio line This amplifier like the other products is limited in number Overview specifications Tube amplifier providing moderate power output levels High quality components and construction throughout 10 W rms per channel rated output into 8 ohm load 12 5 W rms peak N...

Page 6: ...oards engineered for top performance Component placement and board traces have been engineered to minimize hum and noise The boards feature a unique mounting technique for the vacuum tubes that keeps heat away from the PWB and minimizes hum in the amplifier The PWBs are designed to reduce off board connections thereby simplifying layout and providing for controlled characteristics from one unit to...

Page 7: ...life Beyond the great specs the amplifier sounds very nice Clean Warm Interesting Like a tube amp should sound The 20 W Stereo Integrated Amplifier is powerful enough to fill a room with great sounding music and small enough to be practical for headphone listening Aside from the obvious application of this product in a home audio system the 20 W Stereo Integrated Amplifier is ideal for use in comp...

Page 8: ...rational Note Unplug the headphones when not in use If left connected the headphones could be damaged by playing the amplifier at high volume using the speakers Headphones typically are not rated for high power operation ...

Page 9: ...or the audio amplifier The output of this stage is direct coupled to the control grid of a triode split load type of phase inverter The use of direct coupling between these stages minimizes phase shift and consequently increases the amount of inverse feedback that may be used without danger of low frequency instability A low noise 6U8A tube V1 V4 which contains a high gain pentode section and a me...

Page 10: ...10 WhitakerAudio Figure 1 1 The 20 W amplifier a amplifier PWB 1 right channel b next page amplifier PWB 2 left channel ...

Page 11: ...11 20 W Stereo Integrated Audio Amplifier Figure 1 1 b ...

Page 12: ...s The second step is to make certain that the components supporting the output tubes are matched as well To this end resistors R6 R7 R9 R10 R11 and R12 for the right channel and resistors R23 R24 R26 R27 R28 and R29 for the left channel are all 1 precision devices In addition coupling capacitors C4 and C5 for the right channel and capacitors C10 and C11 for the left channel are all 5 tolerance dev...

Page 13: ...nt per plate is 500 mA Bias voltage has a significant impact on the steady state current requirements of the amplifier stages An operating value of 30 V is strongly recommended Lower less negative bias will result in shorter tube life from the output devices and rectifier Fixed bias operation of the output stage requires that the power supply provide good voltage regulation as the plate current of...

Page 14: ...nd power supply filter circuits The daughter board shown in Figure 1 2b contains a buffer amplifier for the Front Aux input The phono preamp is a three stage high gain circuit intended for use with a magnetic phonograph pickup device A nominal load of 47 kΩ is assumed for the phono cartridge An input signal of 0 0055 V rms at 1 kHz provides approximately 1 V output from the stage which is 13 dB be...

Page 15: ...15 20 W Stereo Integrated Audio Amplifier Figure 1 2 Transistorized stereo preamplifier a main PWB and chassis mounted components b next page daughter board PWB ...

Page 16: ...16 WhitakerAudio Figure 1 2 b ...

Page 17: ...s achieved with an input of 1 V rms at 1 kHz applied to the input terminals of the circuit CONN103 with the tone control potentiometers set for flat response The nominal output operating level is 1 V rms At this level THD is less than 0 3 percent IMD is 0 01 percent or less Noise is 75 dB or better Potentiometers R156 and R157 provide an adjustable output of the tone control circuit for the right ...

Page 18: ...d to operate reliably at normal room temperature If operated at an elevated temperature component damage or shortened tube life could result This feature shuts down the amplifier if the temperature inside the chassis exceeds 170 F This is well below the maximum rated operating temperature of the amplifier components Under Voltage Shutdown The power supply is designed to operate reliably under a wi...

Page 19: ...201 through Q203 and associated components2 The basic circuit gives a time delay from a few seconds to several hours With the circuit components chosen for this implementation a range of about two hours 15 minutes can be selected through setting of R209 Delay Adjust Clockwise rotation of R209 increases the delay time The timing interval is initiated by applying power to the circuit At the end of t...

Page 20: ...20 WhitakerAudio Figure 1 3 Power management circuit for the 20 W integrated stereo amplifier ...

Page 21: ... the 20 W Stereo Integrated Amplifier shown in Figure 1 1a illustrates the power management system as a black box device with two input terminals and two output terminals The system is best thought of in this way When all operating conditions are satisfied the power management PWB functions as a piece of wire connecting the ac input power to the rest of the amplifier When an out of tolerance condi...

Page 22: ... convention cooling is adequate so long as airflow around the amplifier is not restricted by other devices shelving etc Because of the large number of interconnecting wires needed for this amplifier expanded sleeving is used where practical to organize the cabling This tends to simplify cable routing and provides for a cleaner appearance Wherever possible cables are dressed either tight to the cha...

Page 23: ...ht Phono Input Left Molex 38720 3202 Molex 38720 3202 Neutrix NF2D 0 88 in 0 13 in Center Neutrix NF2D 0 88 in 0 13 in Center 20 W Stereo Integrated Amplifier Neutrix NF2D 0 88 in 0 13 in Center Neutrix NF2D 0 88 in 0 13 in Center AC connector shell 0 75 in x 1 08 in Center 0 15 in Figure 1 5 The back panel of the 20 W Stereo Integrated amplifier ...

Page 24: ...ption Quantity Manufacturer Part Number Allied Stock No C1 C7 47 μF 450 V electro lytic 2 Illinois Capacitor 476TTA450M 70111929 C2 C4 C5 C8 C10 C11 0 22 μF 400 V 5 6 Vishay 715P22454MD3 70079372 C3 C9 3 3 pF 1000 V ceramic or mica 2 Vishay 561R10TCCV33 70079828 C6 C12 200 pF 1000 V ceramic or mica 2 Vishay 562R10TST20 70079438 C13 C14 20 pF 1000 V ceramic 2 Vishay 561R10TCCQ20 70079497 C16 C18 C5...

Page 25: ...X1H473KTP 70188291 C112 C120 0 0022 μF 100 V poly ester 2 Nichicon QYX2A222KTP 70188281 C113 C114 C121 C122 10 μF 25 V electrolytic 2 Vishay TE1204 E3 70079640 C124 1 000 μF 35 V elec trolytic 1 Vishay MAL213816102E3 70122981 C125 4 700 μF 63 V electro lytic 1 Cornell Dubilier 381LX472M063A022 70190438 C127 C128 C129 C130 C135 10 μF 50 V tantalum 5 Vishay 199D106X0050F6V1E 3 70212708 C201 C207 500...

Page 26: ...FB14 70200352 R14 R15 R31 R32 4 Ω 10 W 4 Ohmite 20J4R0E 70023134 R16 R17 R33 R34 27 Ω 2 W 4 Ohmite OY82GKE 70024451 R37 R42 R51 R52 220 kΩ 2 W 4 Ohmite OY224KE 70022218 R53 270 kΩ 2 W 1 Ohmite OY274KE 70024452 R54 R56 47 kΩ 2 W 2 Ohmite OY473KE 70024456 R55 100 Ω 2W potentiom eter 1 Honeywell Clarostat RV4LAYSA101A 753 1001 R57 5 kΩ 2 W potentiom eter 1 Honeywell Clarostat RV4LAYSA502A 70153104 R5...

Page 27: ...154094 R141 R144 R210 150 Ω 2W 3 Ohmite OY151KE 70022208 R121 10 kΩ linear taper potentiometer dual gang panel mount 1 Precision Electronic Components KKU1031S28 DigiKey R122 10 kΩ audio taper potentiometer dual gang panel mount 2 W 1 Precision Electronic Components KKA1031S28 DigiKey R123 R134 R152 R153 R160 R167 100 kΩ 0 5 W 6 Ohmite OL1045E 70022920 R124 R135 R150 R151 R161 R168 20 kΩ 0 5 W 6 R...

Page 28: ... Bourns 3386F 1 103LF 70154071 R201 8 2 mΩ 0 5 W 1 TE Connectivity CFR50J8M2 70063357 R202 15 mΩ 0 5 W 1 Vishay VR37000001505 JR500 70121881 R203 R206 R212 150 Ω 0 5 W 3 RCD GP60 1500 FTW 70183681 R204 430 kΩ 0 5 W 1 RCC RCC050 430K J 70276441 R205 33 Ω 0 5 W 1 Ohmite OL3305E 70023830 R207 1 kΩ 2 W 1 Ohmite ON1025E 70022958 R209 2 mΩ PC mount potentiometer 1 Bourns 3386P 1 205LF 70154217 R211 15 k...

Page 29: ...r 1N5359BG 70099710 D102 Zener 28 V 5 W 1 ON Semiconductor 1N5362BG 70099711 D201 100 V switching diode 1 Philips Semi 1N4148 113 70012012 D202 D204 D205 D206 Rectifier diode 1 A 600 V 4 NTE NTE116 70214755 D203 Zener 25 V 5 W 1 ON Semiconductor 1N5360BG 70099659 D207 Zener 15 V 5 W 1 ON Semiconductor 1N5352BG 70099706 D208 Zener 22 V 1 W 1 Vishay 1N4748A TR 70061622 CR51 CR201 Bridge rectifier 10...

Page 30: ...relay 3 Omron MY2DC24 S 70178955 RYL202 RYL204 DPDT 10 A 120 V ac relay 2 Omron MY2AC110 120 S 70178951 Relay sockets 5 Omron PY08 02 70179037 PL51 115 V ac pilot lamp 1 Dialight 249 7841 1431 574 70081495 L51 Choke 5 H 300 mA dc resistance 57 Ω 1 Hammond 193L Allied spe cial order T1 T2 Output transformer Primary 6600 W plate to plate 20 W Secondary 4 8 16 Ω 2 Hammond 1620A Allied spe cial order ...

Page 31: ... inch 2 Keystone 617 70181679 TB3 TB4 4 terminal barrier strip 2 Molex 38720 6204 70110965 TB1 TB2 Speaker output termi nals 2 Molex 38720 3202 70110957 J2 inch stereo head phone jack 1 Switchcraft 112BX 70214271 J1 J105 3 5 mm connector 2 Kobiconn 161 3402 E Mouser 161 3402 E Amplifier PWB 1 right 1 ExpressPCB custom Amplifier PWB 2 left 1 ExpressPCB custom Rectifier PWB 1 ExpressPCB custom Speak...

Page 32: ...churter 6100 3300 70080620 2 terminal Molex header 2 Molex 22 03 2021 70190628 2 terminal Molex housing 2 Molex 22 01 2021 70190672 4 terminal Molex header 11 Molex 22 03 2041 70190629 4 terminal Molex hous ing 11 Molex 22 01 2041 70190701 12 terminal Molex header 2 Molex 22 03 2121 70190653 12 terminal Molex housing 2 Molex 22 01 2127 70190641 Molex crimp terminal 64 Molex 08 50 0114 70190615 F10...

Page 33: ...6 black stranded 2 ft Primary wire 16 white stranded 2 ft Primary wire 16 green stranded 20 ft Expandable sleeving small 10 ft Expandable sleeving large 4 ft Heat shrink tubing small 2 ft Heat shrink tubing large 6 Spade terminal 6 screw 22 wire 6 Quick disconnect female miniature 22 wire 4 Butt splice connector 22 wire 6 Ground lug terminal 4 screw 8 Ground lug terminal 6 screw 64 Phillips head s...

Page 34: ...n inside diameter 8 Phillips head screw 8 3 8 inch 8 Lockwasher 8 7 3 8 inch flat washer 5 Grommet 0 5 in mounting hole 2 Grommet 0 75 in mounting hole 11 Cable clamp 1 2 inch 10 Tie wrap small 10 ft Rosin core solder 9 Vinyl pads self adhesive 1 Press on heatsink 3 caution stickers acrylic conformal coating MG Chemicals 419C 340G Table 2 2 Consumables for the 20 W Stereo Integrated Amplifier ...

Page 35: ...ncludes a main board and daughter board The power management module which is a single board Each of these modules are described in the following sections 3 1 20 W Stereo Amplifier Module A printed wiring board PWB implementation is used that incorporates all components of the stereo amplifier except for the transformers which are mounted on the chassis The amplifier module includes amplifier board...

Page 36: ...ND Ground Shield Ground FB Audio input to amplifier White Connects to output of right channel preampli fier board GND Ground NC GND Ground NC TB3 4 terminal barrier strip 1 350 V dc B supply input Red Connects to TB4 terminal 1 on Amplifier PWB 2 left 2 GND Black Connects to TB4 terminal 2 on Amplifier PWB 2 left 3 Bias supply input Slate Connects to TB4 terminal 3 on Amplifier PWB 2 left 4 GND Bl...

Page 37: ... Connects to pilot light PL51 NC Not connected Blue yellow Connects to blue yellow primary lead from T51 NC Not connected Brown yellow Connects to brown yellow primary lead from T51 NC Not connected Black red Connects to black red primary lead from T51 NC Not connected White black Connects to the white black primary lead from T51 NC Not connected NC NC Not connected NC GND Ground Black Connects to...

Page 38: ...38 WhitakerAudio Figure 3 1 Component layout for the Amplifier PWB 1 right board ...

Page 39: ...onnects to 6VH1 post on Amplifier PWB 2 left 6VH2 6 V ac heater connection Green Connects to green lead from T51 6VH2 6 V ac heater connection Brown Connects to 6VH2 post on Amplifier PWB 2 left 6VHct 6 V ac heater center tap Green yellow Connects to green yellow lead from T51 400V Plate voltage input Red Connects to red lead from T51 400V Plate voltage input Red Connects to red lead from T51 T51c...

Page 40: ...40 WhitakerAudio Figure 3 2 Rectifier PWB component layout ...

Page 41: ...Audio input to amplifier White Connects to output of left channel preamplifier board GND Ground NC GND Ground NC TB4 4 terminal barrier strip 1 350 V dc B supply output Red Connects to TB3 terminal 1 on Amplifier PWB 1 right 2 GND Black Connects to TB3 terminal 2 on Amplifier PWB 1 right 3 Bias supply output Slate Connects to TB3 terminal 3 on Amplifier PWB 1 right 4 GND Black Connects to TB3 term...

Page 42: ... RYL51 RYL51 Voltage source to RYL51 coil White Connects to coil of RYL51 GND Ground Black Connects to ground terminal on rectifier PWB GND Ground Black Connects to main chassis ground point 6VH1 6 V ac heater Green Connects to the 6VH1 post on Rectifier PWB 6VH2 6 V ac heater Green Connects to the 6VH1 post on Rectifier PWB PL1 Plate from V5 Blue Connects to blue lead from T2 SC1 Screen from V5 B...

Page 43: ...43 20 W Stereo Integrated Audio Amplifier Figure 3 3 Component layout for the Amplifier PWB 2 left board ...

Page 44: ...n before proceeding PWB Code Function Connection Color Code Notes GND Chassis ground Black Connected to main ground point T1com Output transformer sec ondary common Black T1 secondary common 4ohm 4 Ω secondary output Green T1 secondary 4 ohm lead 8ohm 8 Ω secondary output Yellow T1 secondary 8 ohm lead 16ohm 16 Ω secondary output White T1 secondary 16 ohm lead SPK GND Common to speaker termi nal B...

Page 45: ...45 20 W Stereo Integrated Audio Amplifier Figure 3 4 Layout of the speaker terminal PWB ...

Page 46: ...odes are detailed in Table 3 5 Table 3 5 Transistorized Preamplifier PWB Connection Wiring Codes PWB Code Function Connection Color Code Notes GND Ground Black Connected to main ground point 40Vdc DC power input Yellow 40 V dc maximum voltage input Connects to V source on power management PWB GND Ground Black Ground connection to pream plifier daughter board V 24 V dc bus Yellow V connection to pr...

Page 47: ...in 5 R132b arm White Pin 6 R132b low Red Pin 7 GND Shield Pin 8 Tone control output left White Pin 9 GND Shield Pin 10 GND NC Pin 11 GND NC Pin 12 CONN 106 on daughter board Left Aux input White Pin 1 Right Aux input White Pin 2 GND Shield Pin 3 GND Shield Pin 4 CONN107 on daughter board Right Aux output White Pin 1 GND Shield Pin 2 Left Aux output White Pin 3 GND Shield Pin 4 24Vdc on daughter bo...

Page 48: ...plifier consists of two PWBs The main board includes the phono preamplifier tone control and power supply filter circuits A second board includes the Front Aux buffer amplifier The layout of the two boards is shown in Figure 3 5 ...

Page 49: ...49 20 W Stereo Integrated Audio Amplifier a b Figure 3 5 Layout of the transistorized preamplifier PWB a main board b daughter board ...

Page 50: ...c line filter FL51 hot terminal Switch1 Front panel power switch Black Connects to front panel power switch SW51 Switch2 Front panel power switch Black Connects to front panel power switch SW51 LoadH Amplifier load hot Black Connects to ac hot for amplifier board 1 Hot 1 SW203 Temperature sensor White Connects to chassis mounted temperature sensor SW203 SW203 Temperature sensor White Connects to c...

Page 51: ...51 20 W Stereo Integrated Audio Amplifier The component layout of the power management board is shown in Figure 3 6 Figure 3 6 Component layout of the power management PWB ...

Page 52: ...rement bridge While this is perhaps overkill it is instructive to see the variation in component values which measurement before installation will reveal The resistor color code is shown in Figure 4 1 Observe proper polarity of devices such as electrolytic capacitors and diodes A distinctive pad usually denotes the positive terminal in the case of an electrolytic The silk screen legend may also pr...

Page 53: ...rrents that will adversely impact the noise floor Efficiently making the socket connections to the PWB requires a bit of practice The recommended procedure is detailed in Section 5 Be certain to wear protective eye glasses during this process and at other steps in PWB assembly The chassis is painted and the transformers are shipped painted To ensure that the case of each transformer is grounded a ...

Page 54: ...t a time as this will reduce the possibility of component mix ups Each section heading that follows marks a logical start stop point in construction of the amplifier Do not rush through the project instead consider setting modest goals for progress over a period of some days A more relaxed pace often results in a better end product and a more enjoyable overall experience Organize a work space that...

Page 55: ...s manual begin populating the circuit boards As the packing envelopes are used set them aside for recycling Before beginning clean the soldering iron tip Install the quick disconnect male tabs using the pads provided on the amplifier board There are 28 positions in all Solder in place Install the quick disconnect male tabs using the pads provided on the rectifier board There are 13 positions in al...

Page 56: ...tor of this component is typically larger than a common 1 2 watt resistor It may be necessary therefore to mount this component about 1 8 inch above the PWB in order to accommodate the leads Install R5 220 kΩ 0 5 W Solder in place Figure 5 1 Recommended procedure for mounting the quick disconnect tabs on the PWB a insert the tap using pliers and carefully work it into the board b position the tab ...

Page 57: ... Install D51 rectifier 2 A 1 kV This diode goes on the rectifier board Solder in place providing about 1 4 inch clearance above the board Be certain to observe proper polarity Note that the banded end of the diode connects to the square pad on the PWB This same convention is used for all other diodes Install VR51 power thermistor 10 Ω cold Solder in place providing about 1 2 inch clearance above t...

Page 58: ...ur corners of the PWB and on each side of each tube socket For the standoff on the corner of the board adjacent to the GND terminal use a 4 ground lug in place of the lockwasher Mount the six standoffs on the foil side of the rectifier board using the 4 40 hardware provided Use a lockwasher on the screw head component side of the board Standoffs are positioned at the four corners of the PWB and on...

Page 59: ...te that only the active pins need be connected at the socket The heater connections are made separately for the amplifier tubes The recommended procedure for installing the connecting wires is as follows 1 Feed a bare wire from the component side through the pad and into the socket soldering tab 2 Crimp in place see Figure 5 2b 3 From the component side pull the wire tight and solder in place a b ...

Page 60: ...cilitate access to the pins Open the Heater Circuit Wire package cut one 9 inch piece of 22 green wire and one 9 inch piece of 22 brown wire Place one piece of heat shrink tubing over one end of each wire Crimp the green wire on pin 4 of V1 Solder in place When soldering make sure the heat shrink tubing is pushed back on the wire so it is not near the soldering point If the heat shrink tubing gets...

Page 61: ...ch wire Crimp the brown wire on pin 5 and then crimp the green on pin 4 Do not solder Cut one 9 inch piece of 22 green wire and one 9 inch piece of 22 brown wire Slip the brown wire through the heat shrink tubing on the lead already connected to pin 5 of V2 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubing away from the hot wires and the soldering iron Slip the gre...

Page 62: ...doff removed from the V3 socket The screws should be finger tight Remember to include the lockwasher on the component side of the board The heater leads should straddle the standoff Twist the wires together and route to the 6V heater pads on the PWB see Figure 5 2d for placement The wires should be placed at socket level Do not dress the wires against the PWB Trim the wire lengths as needed to com...

Page 63: ...ormal coating MG Chemicals 419C 340G may be applied to the foil side of the amplifier and rectifier PWBs Use masking tape to cover the face of the tube sockets Assembly of the 20 W Stereo Amplifier PWB 1 Right Channel now been completed The finished board is shown in Figure 5 3 Check the PWB for proper installation of all components Look for bad solder connections or solder splash that might cause...

Page 64: ...64 WhitakerAudio a b Figure 5 3 Completed 20 W Stereo Amplifier PWB 1 module a amplifier component side b amplifier foil side c rectifier component side d rectifier foil side c d ...

Page 65: ...on tip Install the quick disconnect male tabs using the pads provided on the board There are 22 positions in all Solder in place Note that the mounting pins fit tight into the board This is normal Use a pair of pliers to hold the tab while inserting the pins into the PWB Make sure the PWB is resting on a soft flat surface while the tabs are installed It is most efficient to install all of the tabs...

Page 66: ...oviding about 1 4 inch clearance above the board Install R53 270 kΩ 2 W Solder in place providing about 1 4 inch clearance above the board Install R54 R56 47 kΩ 2 W Solder in place providing about 1 4 inch clearance above the board Install R59 270 Ω 2 W Solder in place providing about 1 4 inch clearance above the board Install R60 3 9 Ω 2 W Solder in place providing about 1 4 inch clearance above ...

Page 67: ...banded end of the diode connects to the square pad on the PWB Install D53 zener 60 V 5 W Solder in place providing about 1 4 inch clearance above the board Be certain to observe proper polarity Install D54 zener 56 V 5 W Solder in place providing about 1 4 inch clearance above the board Be certain to observe proper polarity Install CR51 bridge rectifier 100 V 2 A Solder in place providing about 1 ...

Page 68: ...amped on the bottom side of the socket Pin 1 on the PWB is identified by a square pad Place the socket in the proper orientation over the PWB so it rests on the standoffs The top of the socket the side the tube plugs into should face outward Loosely tighten the mounting screws See Figure 5 2a Install connecting wires from the PWB pads to the tube socket pins Solder in place Materials for these ste...

Page 69: ... green wire and one 9 inch piece of 22 brown wire Place one piece of heat shrink tubing over one end of each wire Crimp the green wire on pin 4 of V4 Solder in place When soldering make sure the heat shrink tubing is pushed back on the wire so it is not near the soldering point If the heat shrink tubing gets hot it will be very difficult to slide into position later Crimp the brown wire on pin 5 o...

Page 70: ...ip the brown wire through the heat shrink tubing on the lead already connected to pin 5 of V5 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubing away from the hot wires and the soldering iron Slip the green wire through the heat shrink tubing on the lead already connected to pin 4 of V5 Route the wire to the pin and crimp in place Solder keeping the heat shrink tubi...

Page 71: ...uld be finger tight Remember to include the lockwasher on the component side of the board The heater leads should straddle the standoff Twist the wires together and route to the 6V heater pads on the PWB see Figure 5 2d for placement The wires should be placed at socket level Do not dress the wires against the PWB Trim the wire lengths as needed to comfortably reach the pads on the foil side of th...

Page 72: ...amplifier PWB Use masking tape to cover the face of the tube sockets Assembly of the 20 W Stereo Amplifier PWB 2 Left Channel has now been completed Check the PWB for proper installation of all components Look for bad solder connections or solder splash that might cause a short circuit The finished board is shown in Figure 5 4 Set the left channel amplifier board aside it will be used later ...

Page 73: ...73 20 W Stereo Integrated Audio Amplifier a Figure 5 4 Completed 20 W Stereo Amplifier PWB 2 Left Channel a component side b foil side b ...

Page 74: ...w apply to the main PWB Parts that are to be installed on the daughter board PWB are identified with an asterisk Install the quick disconnect male tabs using the pads provided on the board There are four positions on the main PWB and two on the daughter board PWB Solder in place Note that the mounting pins fit tight into the board This is normal Use a pair of pliers to hold the tab while inserting...

Page 75: ...168 20 kΩ 0 5 W Solder in place Install R125 R136 R154 R155 R162 R169 6 8 kΩ 0 5 W Solder in place Find R146 R147 6 8 kΩ 0 5 W Set these components aside They will be installed later Install R126 R137 R163 R170 470 Ω 0 5 W Solder in place Install R129 R131 R133 R139 R142 R143 R148 R149 5 6 kΩ 0 5 W Solder in place Install R130 R140 39 kΩ 0 5 W Solder in place Install R141 R144 150 Ω 2 W Solder in ...

Page 76: ...lace Install C112 C120 0 0022 µF 100 V polyester Solder in place Install C113 C114 C121 C122 10 µF 25 V electrolytic Solder in place observing proper polarity Install C123 C126 C136 0 01 µF disc 1 kV Solder in place Install C124 1 000 µF 35 V electrolytic Solder in place observing proper polarity Install C125 4 700 µF electrolytic 63 V Insert this component into the PWB and then bend the pins to t...

Page 77: ...o 4 terminal Molex contact headers at the CONN102 and CONN103 positions Solder in place It may be necessary to hold the header in place from the component side of the board until the first terminal is soldered Mount the two 4 terminal Molex contact headers at the CONN106 and CONN107 positions on the daughter board PWB Solder in place It may be necessary to hold the header in place from the compone...

Page 78: ...preamplifier section of the PWB The order of the hardware is as follows 1 4 inch 4 screw lockwasher daughter board M F standoff lockwasher PWB F F standoff Tighten Mount the remaining five standoffs on the foil side of the board using 4 40 hardware provided Use a lockwasher on the screw head component side of the board Standoffs are positioned at the four corners and lower center of the PWB For th...

Page 79: ...udio Amplifier a b Figure 5 5 Completed preamplifier PWBs a main board with daughter board attached b main board with daughter board removed c main board foil side d daughter board component side e daughter board foil side c d e ...

Page 80: ... on the board There are 13 positions in all Solder in place Note that the mounting pins fit tight into the board This is normal Use a pair of pliers to hold the tab while inserting the pins into the PWB Make sure the PWB is resting on a soft flat surface while the tabs are installed It is most efficient to install all of the tabs and then turn the board over and solder in place Be careful to not d...

Page 81: ...he positive terminal is denoted by the square mounting pad Install C202 1000 pF 100 V Solder in place Install C203 0 047 µF 100 V Solder in place Install C204 C205 1 000 µF 50 V electrolytic Solder in place observing proper polarity Install C206 0 01 µF disc 1 kV Solder in place Note that D201 and the other semiconductors installed in the steps that follow are sensitive to static discharge Take ap...

Page 82: ...y align the leads of the device Be careful when soldering to avoid creating solder bridges between the leads Install the press on heat sinks on Q203 and Q206 Note that one side of the heat sink is split Using a small screwdriver spread the fins slightly while pushing the heat sink on to the device Install Q203 Q206 C9F NTE5408 Solder in place Be certain to properly align the leads of the device Ma...

Page 83: ... mount flat against the PWB Install the fuse holder using the 4 hardware provided Use short bare connecting wires from the terminals to the pads on the PWB Solder in place Tighten the set screw do not over tighten A method that works well for the above step is to first mount the fuse block with the hardware finger tight Then feed the bare wire up from the foil side of the board and affix it to the...

Page 84: ...84 WhitakerAudio Figure 5 6 Power management PWB a component side b foil side a b ...

Page 85: ...ace A full size image of the completed chassis bottom view is provided Refer to this image as you complete the steps that follow A few general comments on wiring are appropriate at this point The chassis accommodates a number of cable clamps to organize wiring within the amplifier In general the following guidelines apply Cable clamps are provided on each side of the chassis 2 each side to accommo...

Page 86: ...nt panel onto the shaft Use one of the nuts to secure the switch chassis panel assembly Do not tighten Find SW202 the Auto Off enable disable switch There are two nuts provided only one will be used Place the lockwasher provided on the shaft Note that one side of the mounting shaft has a key this key should face downward Insert the switch into the chassis and then fit the front panel onto the shaf...

Page 87: ...ter dual gang panel mount Note that there is a key tab at the base of the potentiometer Using the pliers bend this tab out of the way Feed the component through the chassis front panel Install a flat washer on the shaft Secure with the nut provided Do not tighten The terminals of the potentiometer should face downward toward the chassis bottom plate Examine the 1 4 inch headphone jack Note that on...

Page 88: ...downward toward the chassis bottom plate Mount pilot lamp PL51 as follows Thread the large mounting nut on the pilot lamp and run down to the base of the threads Place the lockwasher provided on the shaft Mount the pilot lamp to the chassis panel and secure with the decorative nut provided Run the decorative nut down to be approximately flush with the mounting shaft From the underside of the chass...

Page 89: ...Secure using the hardware provided Install the remaining 35 mm jack in the available Auxiliary Input opening on the front panel Secure using the hardware provided Install a large knob on the Volume potentiometer Using a small common screwdriver run the set screw out so the knob will fit on the shaft Set the potentiometer to the full counterclockwise position Place the knob on the shaft and set to ...

Page 90: ...upward toward the head of the screw Insert the screw into the back panel hole so the screw protrudes out of the back chassis Install a lockwasher on the screw and then the lock tight nut Spread the ground lugs on the inside of the chassis so they can be used individually Tighten the lock tight nut Install two flat washers on the screw and then the wing nut Tighten the wing nut finger tight The fin...

Page 91: ... installed The back panel is shown in Figure 5 9 5 5 3 Cable Clamps and Related Hardware Some of the cable clamp mounting screws will not be accessible after the PWBs have been installed Therefore they need to be installed first Three of the screws that hold the cable clamps also serve as mounting posts for the acrylic cover See the chassis layout drawing in Figure 5 10 Note the locations of the c...

Page 92: ... for the acrylic cover Note also one end of the device is marked line This end should face the rear panel Secure the rear facing end of FL51 using the 6 hardware provided Include a ground lug between the mounting tab and the nut on the Line side Note that the mounting tab may be notched to permit easier assembly With a notch in the mounting tab the screw ground lug nut can be started and then the ...

Page 93: ...mp Cable clamp Hammond 193L 0 5 in 0 2 in Hammond 378X 0 75 in 0 2 in 0 188 in Qualtek RFI Filter Right Line input Left Built in California USA Right Channel Ground 8 Ohms Left Channel 8 Ohms Ground Right Phono Input Left Molex 38720 3202 Molex 38720 3202 Neutrix NF2D 0 88 in 0 13 in Center Neutrix NF2D 0 88 in 0 13 in Center 20 W Integrated Stereo Amplifier Neutrix NF2D 0 88 in 0 13 in Center Neu...

Page 94: ...ifier circuit board Do not tighten the screws until all screws have been threaded Locate the Amplifier PWB 1 right assembly Remove the screws that secure the sockets to the standoffs and remove the screws in the standoffs at the four corners of the PWB if present Set these in a convenient place Check the heater wiring on the foil side of the board Position so the wiring will rest against the chass...

Page 95: ...chassis cutouts so they are flush with the top of the chassis Locate the Rectifier PWB Remove the screws that secure the socket to the standoffs and remove the screws in the standoffs at the four corners of the PWB if present Set these in a convenient place Carefully place the rectifier PWB in position from the underside of the chassis Make sure the board is properly oriented See Figure 5 10 for g...

Page 96: ...ker and apply it to the under side of the chassis in the approximate location of the transformer This will serve as a reference for connections and service at a later point if needed Locate the power transformer T51 Examine the mounting holes Note that two additional holes are provided within the confines of the base of the transformer These holes are used for the support standoffs for the power m...

Page 97: ...h the choke leads All of the transformers have now been installed 5 5 6 Install Remaining Chassis Components Locate the remaining chassis mounted components which include the following Panel mount potentiometers R55 and R57 Top chassis decal Mount R55 100 Ω potentiometer Hum Balance Control Note the tab extending from the component toward the front of the device Using a pair of long nose pliers be...

Page 98: ...p of the chassis behind tubes V5 and V6 Apply the decal 5 5 7 Wire the Transformer Leads Find the female quick disconnect connectors In the following steps the transformer leads will be connected to their respective terminals on the circuit boards using these connectors The lead lengths from the various transformers may need to be trimmed to remove excess length Make sure to keep sufficient lead l...

Page 99: ...inch piece of large sized sleeving onto the secondary leads of the right channel output transformer T1 Be sure to include the black ground wire from the transformer case Position one end of the sleeving near the base of the transformer where the leads enter the chassis Stretch the sleeving to its full length Place one piece of heat shrink tubing on each end of the sleeving Process with the heat gu...

Page 100: ... T51 yellow yellow yellow black Include the black ground wire from the transformer case Position one end of the sleeving near the base of the transformer where the leads enter the chassis Stretch the sleeving to its full length Place one piece of heat shrink tubing on each end of the sleeving Process with the heat gun Be careful to focus the heat on the heat shrink tubing not the sleeving This cab...

Page 101: ...put transformer plate 2 connection Find the brown wire from the right channel output transformer Install a connector to the end of the wire Attach to the PL2 post on the right channel PWB Connect SC2 output transformer screen 2 connection Find the brown yellow wire from the right channel output transformer Install a connector to the end of the wire Attach to the SC2 post on the right channel PWB C...

Page 102: ...Connect T2ct output transformer center tap Find the red wire from the left channel output transformer Install a connector to the end of the wire Attach to the T2ct post on the left channel PWB Double check the connections from the left channel output transformer to the PWB 5 5 7 4 Power Transformer Leads In the following steps trim the transformer lead lengths so the wires will comfortably reach t...

Page 103: ...of 120 V ac Connect N 2 AC neutral to T51 Find the brown lead from the power transformer Install a connector to the wire Attach to the N 2 post on the right channel PWB Route the wire below the cable to output transformer T1 Connect N 3 AC neutral to T51 Find the white lead from the power transformer Install a connector to the wire Attach to the N 3 post on the right channel PWB Route the wire bel...

Page 104: ...to a lead gently pull on the wire and terminal to make sure a good crimp has been made Connect B choke in Find one of the black wires from the power supply choke L51 Check to see if the lead will comfortably reach the B terminal on the rectifier PWB If it will install a connector to the wire Attach to the B post on the rectifier PWB In the event that the lead is not long enough to reach the B post...

Page 105: ...late wire and a 4 inch long slate wire Combine the wires and attach a spade terminal Connect to the 3 terminal on the right channel PWB barrier strip TB3 Bend the barrel up to near vertical and orient the spade terminal to face the front of the chassis Feed the free end of the long white wire to the left channel PWB through the cable clamps at the rear of the chassis Attach a quick disconnect term...

Page 106: ... wires and install a connector Attach to the 6VH2 post on the rectifier PWB Attach a spade terminal to the free end of the slate wire Connect to the 3 terminal on the left channel PWB barrier strip TB4 Bend the barrel up slightly and orient the spade terminal to face the front of the chassis Cut a 22 inch long 22 red 600 V wire Combine this wire with the free end of the red wire from the right cha...

Page 107: ...8 inch long 18 black wire Secure one end to the ground lug on the corner of the rectifier PWB Solder 2 wires Route the free end of the 18 inch 18 black wire to the back panel ground lug that contains the black wire from the right channel PWB Do not solder Route the wire through one of the cable clamps in the rear portion of the chassis Prepare a 13 inch long 18 black wire Secure one end to the gro...

Page 108: ... detailed in the steps below Cut a 1 inch long piece of 18 black wire Using a soldering iron and small amount of solder tin one end of the 18 black wire and tin one lead from VR53 Bring the two tinned wires together and solder forming a reliable solder bridge Cut a 1 inch piece of small heat shrink tubing Place over the splice point and process heat Observe the rear of the ac power connector There...

Page 109: ...ach the other end of the black wire with the VR53 lead to the terminal of circuit breaker CB51 closest to the chassis deck Using the primary ac wire included in the AC Power Connector Hardware package prepare a 4 inch piece of 16 black stranded wire Attach a connector to each end of the wire Attach one end of the black wire to the line terminal on the ac power connector Attach the other end of the...

Page 110: ...ir miniature connectors to the mating coil posts on RYL51 Attach one of the standard size connectors to the RYL51 post on the left channel PWB Attach the other connector to the RYL51 post Use the available cable clamps for routing Prepare one 21 inch long 22 white wire Attach a quick disconnect terminal to one end of the wire Attach to the N 4 AC neutral to PL51 post on the right channel PWB Route...

Page 111: ...wire at one end Connect the brown wire terminal to the R55a post on the left channel PWB Connect the green wire terminal to the R55b post on the left channel PWB Using the available cable clamp route the green brown twisted pair to Hum Balance control R55 which is located at the rear of the chassis adjacent to the back panel Trim the wire lengths if needed Secure the brown wire to terminal 1 of R5...

Page 112: ...he R57b post on the left channel PWB Route the other end of the wire through the nearby cable clamp to the rear of the chassis Connect the wire to the low terminal of R57 terminal 1 Solder in place Prepare one 19 inch 22 slate wire Install a quick disconnect connector on one end Connect R57arm R57 arm terminal Attach the 22 slate wire prepared in the previous step to the R57arm post on the left ch...

Page 113: ...o the available terminal on the front panel Speaker On Off switch SW52 Do not solder Install VR55 18 V varistor Connect one lead to each terminal on the front panel Speaker On Off switch SW52 Solder 2 wires per terminal It may be helpful to use a short piece of spaghetti on each lead Dress the wiring against the chassis Route the free end of the yellow wire to the back panel through the cable clam...

Page 114: ...quick disconnect connector to each of the four leads include the ground wire from the transformer case with the black lead 5 5 11 2 Speaker PWB Assembly Find the speaker terminal PWBs Two are provided one for the right channel and one for the left channel Each board mounts on the speaker terminals for the respective channel Temporarily fit each PWB on to the speaker terminals The board should fit ...

Page 115: ...Install R31 and R32 on the left channel speaker PWB Place a 4 Ω 10 W resistor in the R load A position and one in the R load B position Mount so the devices are about 1 2 inch above the PWB Solder both devices in place Install R33 and R34 27 Ω 2 W on the left channel speaker PWB Solder Install C6 200 pF on the right channel speaker PWB in the position Cfb Solder in place Install C12 200 pF on the ...

Page 116: ...ions Because the right channel speaker PWB is rotated relative to the left channel board speaker connections will be made to the right channel prior to the board being soldered into position Note When making connections to the speaker terminal PWBs support the board as needed to avoid stressing the PWB Find the black common lead from the right channel output transformer Connect the terminal to the...

Page 117: ...trip post and the PWB mounting post Use care when soldering to avoid contact with other wiring in the chassis and or the relay housing Cut a 4 inch long 18 yellow wire Attach a quick disconnect terminal to one end of the wire Using a pair of long nose pliers fashion a small loop at the other end of the wire Attach to the right channel 8 Ohm terminal from the component side of the PWB Solder Note t...

Page 118: ...erminal to one end of the wire Using a pair of long nose pliers fashion a small loop at the other end of the wire Attach to the left channel 8 Ohm terminal from the component side of the PWB Solder Note that the solder connection ties together the yellow wire the barrier strip post and the PWB mounting post Use care when soldering to avoid contact with other wiring in the chassis and or the relay ...

Page 119: ...reamplifier and right channel speaker PWBs Solder 3 wires Attach a quick disconnect terminal to the free end of the 8 inch 18 black wire Attach to one of the GND post on the left channel speaker PWB Find the 4 inch long 18 black wire from the right channel speaker terminal Attach to the SPK GND post on the right channel speaker terminal PWB Find the 4 inch long 18 black wire from the left channel ...

Page 120: ...ellow wire Attach a quick disconnect terminal on each end Attach one end of the yellow wire just assembled to the COM post on left channel speaker relay RYL2 Attach the other end to the OUT post on the left channel speaker PWB Find the black common lead from the left channel output transformer Connect the terminal to the T1com post on the left channel speaker PWB Find the green 4 Ω lead from the l...

Page 121: ...d the1 4 inch headphone jack J1 Make the following connections White to the ring terminal on J1 Solder Black to the tip terminal on J1 Solder Shield to the sleeve terminal on J1 Solder Prepare a 19 inch long 2 conductor shielded cable Remove 4 inches of insulation from one end and 2 inches of insulation from the other end Attach a quick disconnect terminal to each of the wires black white and shie...

Page 122: ...e left channel output barrier strip on the back panel The ohmmeter should read 0 ohms Connect the red lead of the ohmmeter to the 8 Ohms terminal on the left channel output barrier strip on the back panel A click should be heard in the left channel headphone The resistance shown on the ohmmeter will be quite low in the neighborhood of 0 5 ohms This is normal Move the headphone plug to the other fr...

Page 123: ...ect to one of the outside terminals on the front panel power switch SW51 Twist the two black wires together Route to the rear of the chassis using the front cable clamp along the left channel PWB Attach quick disconnect terminals to the ends of each wire Prepare a 26 inch long 22 blue wire Attach one end of the wire to the center terminal of the front panel Auto Off switch SW202 Solder Prepare a 2...

Page 124: ...t shrink tubing may be placed over the connection points Solder Twist the wires together Prepare a 14 inch long 22 black wire Attach a quick disconnect terminal to one end of the wire Attach to the GND post in the center of the power management PWB The other end of the wire will be connected later Prepare a 17 inch long 16 stranded white wire Attach quick disconnect terminals to each end of the wi...

Page 125: ... the GND post on the power management PWB Find the 22 white twisted pair wires from over temperature switch SW203 Connect the wires to the SW203 posts on the power management PWB Insert the 4 terminal Molex connector on the CONN201 post on the power management PWB The blue wires go to terminals 3 and 4 Check the position of R209 It is typically set for center rotation which provides an auto off de...

Page 126: ...Cut a 10 inch long 22 black wire Attach quick disconnect terminals to each end of the wire Connect one end of the wire to the GND post on the preamplifier PWB Cut a 13 inch long 22 blue wire Attach quick disconnect terminals to each end of the wire Connect one end of the wire to the V post on the preamplifier PWB Twist the blue and black wires together and route toward the preamplifier daughterboa...

Page 127: ...cable Attach connector pins to each of the two wires on one end of the audio cable Insert the connector pins into the socket housing as follows shield to position 1 and white to position 2 Cut two short pieces of small heat shrink tubing each about 3 4 inch long Place the tubing at each end of the audio cable Process Insert the Molex socket into the Conn1 connector on the right channel PWB Note th...

Page 128: ...nd of the audio cable For the end of the cable inserted into the Molex connector process apply heat after the wires have been inserted into the connector but before the cable is installed in the amplifier Hardware for the following steps can be found in the 2 4 12 Terminal Molex Housing and Terminals package Examine the Molex socket housing The connector pins insert one way only As each connector ...

Page 129: ...t the other 2 pin Molex socket into the CONN100 connector on the preamp PWB Connect the cable from the CONN100 terminal to the Right Channel Phono Input jack on the back panel The white wire goes to the center pin and the shield goes to the shell Solder Prepare a 28 inch long audio cable Cut two short pieces of small heat shrink tubing each about 3 4 inch long Place the tubing at each end of the a...

Page 130: ...ight position on the switch Do not solder Note that positions 4 6 right on SW101 are not used as inputs but instead will be as a shield termination point Connect the white wire of the free end of the Right Channel Line Input cable to the 2 right position on front panel Input Switch SW101 Solder Connect the shield to the 4 right position on the switch Do not solder Prepare an 18 inch long audio cab...

Page 131: ...short pieces of small heat shrink tubing each about 3 4 inch long Place the tubing at each end of the audio cable Process Prepare an 18 inch long audio cable Attach connector pins to each of the two wires the white wire and the shield on one end of the audio cable Insert the connector pins into the 4 conductor Molex socket housing as follows white to position 3 and shield to position 4 Insert the ...

Page 132: ...e end of the wire to the arm right position on SW101 Solder Leave the other end free for now Connect the cable from the 2 4 position on Conn2 to SW101 The white wire goes to position 1 left Solder The shield goes to position 4 Solder 2 wires Prepare a 2 inch long 22 white wire Connect one end of the wire to the arm right position on SW101 Solder Leave the other end free for now Check the orientati...

Page 133: ...nect the other end to terminal 3 high on Volume Control R122b Solder Prepare a 3 inch long 22 black wire Connect one end to terminal 2 arm of Balance Control R121a Solder Connect the other end to terminal 1 low of Volume Control R122a Do not solder Prepare a 3 inch long 22 black wire Connect one end to terminal 2 arm of Balance Control R121b Solder Connect the other end to terminal 1 low of Volume...

Page 134: ...ps organize the audio cabling into a bundle and route along the side of the chassis Prepare a 24 inch long piece of 3 conductor audio cable Attach crimp terminals to the red white black and shield wires on one end of the cable Insert the crimped terminals into a 12 terminal Molex header as follows Black to pin 1 R127a high White to pin 2 R127a arm Red to pin 3 R127a low Shield to pin 4 GND Cut two...

Page 135: ...9 right output Shield to pin 10 GND Using a heat gun process the heat shrink tubing on the end of the cable Prepare a 12 inch long 22 black wire Attach a connector pin to one end of the wire Insert into the 12 terminal Molex header as follows black to pin 12 GND Insert the 12 terminal Molex connector just assembled into CONN104 on the preamplifier PWB Note that pin 1 faces the rear of the chassis ...

Page 136: ... pieces of heat shrink tubing Slip one piece over each end of the audio cable Process being careful to not use too much heat Prepare a 25 inch long piece of 3 conductor audio cable Attach crimp terminals to the red white black and shield wires on one end of the cable Insert the crimped terminals into the 12 terminal Molex header as follows Black to pin 5 R127a high White to pin 6 R127a arm Red to ...

Page 137: ...105 on the preamplifier board Route the cable to the front panel Bass Control Connect the wires to R127b as follows Red to terminal 1 low Solder White to terminal 2 arm Solder Black to terminal 3 high Solder Clip off the shield drain wire It is not used on this end Find the cable from terminals 5 8 of CONN105 on the preamplifier board Route the cable to the front panel Treble Control Connect the w...

Page 138: ... 20 W Stereo Integrated Amplifier has now been completed Make a thorough visual inspection to make sure everything looks OK All parts should be installed with the exception of the vacuum tubes If you have any parts left over recheck the procedures documented here and install the part s as needed Figure 5 14 shows the chassis view of the 20 W stereo integrated amplifier Various detail views of the ...

Page 139: ...WB inside the chassis Danger High Voltage on the power management PWB foil side avoid line traces Before proceeding to Initial Checkout it is recommended that builders clean up the workspace and put away all tools An occasional workbench reset is useful for any project Figure 5 14 Chassis view of the 20 W Stereo Integrated amplifier ...

Page 140: ...140 WhitakerAudio Figure 5 15 Detail views of the 20 W Stereo Integrated amplifier a preamplifier PWB b power management PWB c right channel and rectifier boards d front panel close up view a b c d ...

Page 141: ... of the ac cord It should be infinity with the power switch off and 4 kΩ with the power switch on 5 Remove the ac power cord from the chassis 6 Using an ohmmeter confirm that the resistance values listed in Table 6 1 are observed All readings are with reference to ground Readings within 5 percent are considered normal For resistance measurements that are influenced by filter capacitors in the circ...

Page 142: ...he pilot lamp V2 V5 6973 1 100 kΩ Varies due to filter capacitors in circuit 2 3 170 kΩ Varies due to filter capacitors in circuit 4 40 kΩ Heater 5 40 kΩ Heater 6 170 kΩ Varies due to filter capacitors in circuit 7 0 Ω 8 100 kΩ Varies due to filter capacitors in circuit 9 100 kΩ Varies due to filter capacitors in circuit V3 V6 6973 1 100 kΩ Varies due to filter capacitors in circuit 2 3 170 kΩ Var...

Page 143: ...time delay is reached the auto off and temperature sense SW203 circuits are enabled by the combination of RYL203 and RYL204 A failure in any of the previous steps will remove power from the amplifier 11 Using extreme caution measure the ac line voltage between ground and the load side of filter FL51 A reading of 120 V ac should be measured on the terminal closest to the side of the chassis to whic...

Page 144: ...he same voltage should be measured at terminal 1 of TB3 on the right channel PWB Typical ac current draw from the ac line is 200 mA The bias voltage at Table 6 2 Typical Voltmeter Readings with V1 V4 V2 V5 and V3 V6 Removed and Power Applied Tube Pin No Typical Reading Notes V1 V4 6U8A 1 460 V 2 0 V 3 430 V 4 60 V Heater 5 60 V Heater 6 460 V 7 0 V 8 0 V 9 460 V V2 V5 6973 1 470 V 2 3 30 V With Bi...

Page 145: ...the tubes for any signs of overheating or other unexpected behavior The filaments should be lit Remove power if any problems are detected or if noticeable hum can be heard from the speaker Recheck wiring and components as needed 22 If oscillation or motorboating is observed immediately remove power from the unit It is important that an oscilloscope be connected to the output terminals in addition ...

Page 146: ...sly for the right channel If oscillations persist install C9 3 3 pF 1000 V ceramic on the left channel PWB The device is typically not required See the cautions above for the right channel equivalent C3 25 If problems are experienced disconnect power and recheck the installation of all components particularly the input stage V1 of the amplifiers With no audio input the amplifier should draw about ...

Page 147: ...l Voltmeter Readings readings within 10 can be considered normal Tube Pin No Typical Reading Notes V1 V4 6U8A 1 205 V 2 0 V 3 40 V 4 60 V Heater 5 60 V Heater 6 80 V 7 1 V 8 80 V 9 80 V V2 V5 6973 1 340 V 2 0 V 3 30 V 4 60 V Heater 5 60 V Heater 6 30 V 7 0 V 8 340 V 9 345 V V3 V6 6973 1 340 V 2 0 V 3 30 V 4 60 V Heater 5 60 V Heater 6 30 V 7 0 V 8 340 V 9 345 V ...

Page 148: ...taken on the amplifier as detailed in the next section Note The amplifier should be operated only with its rated load applied Operation into an open circuit or short circuit load can result in damage to components 6 1 Power Management System Issues Operation of the power management system is essentially invisible As long as any of the trip points are not present the overall system will perform as ...

Page 149: ... Remove the four screws from the power management PWB Using the L angle brackets mount the board at a right angle to the chassis deck using the available 6 hardware Be careful to not stress the board while mounted in this way as it could crack the edge of the PWB Important the brackets should rest against the component side of the board If mounted with the brackets against the foil side of the boa...

Page 150: ...he amplifier Set the Delay Adj trimmer potentiometer for center of travel This should result in a time out period of about two hours which is a good starting point Position the Auto Off switch to the On position Switch the amplifier off and remove the power cord from the ac outlet After confirming that the B supply has discharged to zero mount the power management PWB on the four standoffs with th...

Page 151: ...es This can be accomplished with the power management PWB in place One of the challenges in checking the operation of the auto off circuit is the long time delay needed to determine if the problem has been fixed about two hours For testing purposes the negative lead of C201 can be unsoldered from the PWB while still in place and a small value capacitor e g 5 μF at 25 V can be tack soldered in plac...

Page 152: ...ending on the gate trigger current tolerance the SCR will not fire after the voltage at the junction of R211 C207 D208 has reached 22 V In this condition the voltage at the gate of Q206 may not increase to much more than 1 V The simplest solution to this problem is to add a high value resistor in parallel to R217 This can be done from the foil side of the board without removing the PWB A range of ...

Page 153: ...right and left channel speakers Touch the center pin of the Phonograph input jacks on the back panel with a small screwdriver A loud hum should be heard as each channel is contacted Switch the front panel Input control to Line and then to Auxiliary No hum or noise should be heard in these positions 6 2 1 Functional Tests The purpose of the following functional tests is to confirm that the amplifie...

Page 154: ...rce devices is wide and varied and as such it may be necessary to select a different reference point depending on the specifics of a given application Operational experience is the best guide here 1 Confirm the front panel settings detailed in the previous section Connect an 8 Ω load to each speaker terminals Connect an audio voltmeter to the right channel output terminals Connect an audio generat...

Page 155: ...typical position for R110 is 2 3rds clockwise 8 Move the signal generator to the Front Aux input jack Apply a 0 3 V rms signal at 1 kHz Set the volume control fully clockwise Set the Balance control to center Switch the Input to Front Aux Adjust the right channel buffer gain control R164 to produce 10 V output at the right channel speaker terminals 9 Move the signal generator to the left channel o...

Page 156: ...e amplifier warms up the surge limiting power thermistor bypass circuit of VR52 and C64 ramps up the voltage to relay RYL51 During a brief portion of this ramp the relay may vibrate slightly however within a few seconds the relay will close The speed of this action is a function of the ambient temperature Check the Speaker On Off function as follows Connect speakers to the amplifier Feed a tone or...

Page 157: ...e preamplifier with an ac voltmeter If a sweep generator is not available use an audio generator set to the frequencies specified below as start and stop points then vary the operating frequency between those points Small variations from the optimal flat response are not unusual between channels Any deviation of more than about 1 dB may be cause for further investigation The following procedure is...

Page 158: ...bserved output on the audio voltmeter should drop by about 12 db Move the Bass control to the full boost position clockwise The observed output on the audio voltmeter should increase by about 12 dB Return the Bass control to the flat position 9 Repeat the previous Bass cut boost measurement on the right channel The performance of the two channels should be identical or at least very close 10 With ...

Page 159: ... the generator to begin the sweep at about 20 Hz and end the sweep at about 20 kHz Begin a repetitive linear sweep of about 1 second duration Observe the right channel performance It should be within about 1 dB 12 Adjust the signal generator to produce a 1 kHz tone at 1 V rms Adjust the Volume control to produce an output of 2 8 V rms at the right channel speaker terminals Set the audio voltmeter ...

Page 160: ...el of 1 kHz must be kept low 1 25 V rms to avoid clipping of the amplifier output on low frequencies which are boosted by the RIAA curve 7 1 2 1 RIAA Equalization The purpose of pre emphasis in vinyl disk recording and the complementary de emphasis in playback is to boost the amplitude of the recorded waveform at higher frequencies to improve the signal to noise ratio S N The emphasis adopted as a...

Page 161: ...and Treble controls are set for their flat positions and the Balance control is centered 3 Adjust the Volume control to produce an output of 1 25 V rms at the speaker terminals Set the audio voltmeter to read 0 dB 4 Using Table 7 1 as a guide adjust the audio generator frequency as needed and observe the response on the voltmeter Readings should agree with the values given in the table within Tabl...

Page 162: ... A reading of below 0 75 percent THD is typical 8 Reduce the output level of the signal generator to 0 0072 V rms Set the frequency of the generator to 1 kHz Adjust the Volume control to produce 2 8 V rms at the speaker terminals Adjust the audio voltmeter so the meter reads 0 dB Remove the generator connector from the right channel phonograph RCA connector and insert a shorting plug Measure the r...

Page 163: ...e of the 20 W Stereo Integrated Amplifier Conditions Parameter Target Value Notes Measurements taken at 1 W power output 2 8 V rms Input voltage 0 30 V rms Volume control fully clockwise Frequency response 1 dB 6 Hz to 55 kHz THD 0 5 Note 1 IMD at 2 3 V rms output 0 5 4 1 mix ratio Noise unweighted shorted input terminals 65 dB Volume control fully clockwise Measurements taken at 5 W power output ...

Page 164: ...ore is often applied e g 81 5 For example since where P power in Watts and R load resistance in Ohms for an IMD measurement at 10 W power output the input signal would be adjusted to yield a measured value at the speaker terminals on an rms reading audio voltmeter of 7 2 V rms 8 9 V times 0 815 The speaker terminal voltages for the IMD measurements at various power levels are shown in Table 7 2 7 ...

Page 165: ... an 8 Ω 15 W load to the output terminals Connect an oscilloscope and audio frequency voltmeter to the output Set the Input switch to Line Input Set the Volume control fully clockwise Apply a 1 kHz signal to the Line input while observing the oscilloscope Find the point at which the top of the trace begins to flatten This is the clipping point Check the oscilloscope trace to confirm that clipping ...

Page 166: ... jack Using the audio voltmeter measure the residual signal which will be a combination of noise and crosstalk from the left channel into the right channel A reading of approximately 75 dB is typical for this amplifier Return the audio voltmeter sensitivity switch to the previous setting 10 W Connect the voltmeter to the left channel output Adjust the meter to read 0 dB Move the 1 kHz signal to th...

Page 167: ...ifier It is important therefore that the controls be set for flat response The following procedure is recommended Apply a 100 Hz square wave signal to the input with the volume control fully clockwise f b c d e a Figure 7 2 Square wave response of the amplifier a 100 Hz at 1 W b 1 kHz at 1 W c 10 kHz at 1 W d 100 Hz at 10 W e 1 kHz at 10 W f 10 kHz at 10 W ...

Page 168: ... Observe the results and compare with Figure 7 2 The following observations can be made regarding typical square wave performance at various power levels and frequencies At 1 W power output a A fair amount of low frequency tilt is observed at low frequencies 100 Hz and below b The response at 1 kHz looks quite good c The response at 10 kHz is respectable with no signs of instability At 10 W power ...

Page 169: ...settings Repeat the process for the left channel The optimal points between channels should roughly coincide Note that some compromises may be necessary to provide for the best relative performance from the right and left channels of the amplifier For a typical implementation the lowest distortion point is usually found to be at a bias of about 25 V dc While varying the bias it may be observed tha...

Page 170: ...r channel Important note The amplifier should never be operated with a bias setting of less than more positive than 20 V Component damage may result It is important to remember that high distortion readings on a given channel can be caused by a variety of issues in addition to the operating bias point If high distortion figures are encountered first try replacing the output tubes and see if that s...

Page 171: ...xcept for the power transformer run at essentially room temperature The power transformer runs warm but not too hot to touch The vacuum tubes are of course quite hot and are capable of inflicting burns on the skin No other areas of the amplifier should run hot Table 7 4 Measured Performance of the 20 W Stereo Integrated Amplifier Conditions Parameter Right Channel Left Channel Measurements taken a...

Page 172: ...over the top Secure with the four 6 screws and flat washers provided Use of the cover is recommended as it serves to protect the tubes from users and users from the tubes It also aids cooling somewhat by creating a chimney effect that collects cool air from the edges of the chassis and exhausts heated air from around the tubes and transformers Do not over tighten the mounting screws If the bottom ...

Page 173: ... can be useful The following sections include performance measurements of the major circuit blocks in isolation Unless otherwise specified the test procedures used to take these measurements are the same procedures detailed previously in this User Manual 7 6 1 Preamplifier Module The preamplifier module consists of three major subdivisions the phono preamp front panel auxiliary input buffer and th...

Page 174: ...4 5 V rms output input 0 027 V rms at 1 kHz Performance Relative to RIAA Curve Frequency Hz input 0 0025 V rms RIAA Curve Target Level dB Measured Level Frequency Hz input 0 0072 V rms RIAA Curve Target Level dB Measured Level dB 20 19 3 20 0 1 000 0 0 30 18 6 18 75 1 500 1 4 1 5 40 17 8 17 75 2 000 2 6 2 7 50 17 0 16 75 3 000 4 7 5 0 60 16 1 16 0 4 000 6 6 6 7 70 15 3 15 0 5 000 8 2 8 2 80 14 5 1...

Page 175: ... unweighted 85 dB Clipping point as observed on an oscilloscope at 1 kHz 5 V rms output input 2 5 V rms Table 7 7 Baseline Performance of Tone Control Preamplifier Measurement Conditions Input signal applied to CONN103 Input voltage 0 3 V rms Frequency 1 kHz Output taken at CONN104 CONN105 Output voltage 1 V rms R156 R157 fully CW V supply voltage 1 28 6 V dc V supply voltage 2 23 9 V dc Parameter...

Page 176: ... Measurements taken at 5 W power out put 6 3 V rms at speaker terminals Input voltage 0 80 V rms Frequency response 1 dB 10 Hz to 50 kHz THD 0 5 IMD at 5 1 V rms output 0 9 Noise unweighted shorted input termi nals 75 dB B current at 5 W output 1 kHz tone 85 mA Measurements taken at 10 W power out put 8 9 V rms at speaker terminals Input voltage 1 0 V rms Frequency response 1 dB 15 Hz to 45 kHz TH...

Page 177: ... match of the output devices will greatly influence THD and IMD performance Also the results given in the table are approximate and an amplifier with any given combination of tubes may perform better or worse than the numbers listed With new tubes selected for a balance of operating characteristics bench testing of the amplifier should yield numbers close to the baseline readings ...

Page 178: ... led to the problem Then the cause of the failure not just the more obvious symptoms will be corrected In high voltage power supplies look for signs of loose connections and overheating Do not overlook the possibility of tube failure Tubes can fail in unpredictable ways and substitution may be the only practical test Troubleshooting through the process of elimination can also be useful This techni...

Page 179: ... wear glasses or other protective eye wear when building or working on electronic equipment Injuries can result from solder splashes cleaning chemicals and other unexpected events When trimming the leads of a component be careful to hold the excess length so that when cut the lead does not fly towards the face Table 9 1 Safety Practices for Working Around High Voltage Equipment Remove all ac power...

Page 180: ...uld drive the triode unit Selected tube parameters are listed in Table 10 1 Table 10 1 Key Parameters of the 6U8A General Characteristics Heater ac dc 6 3 V 0 45 A Heater cathode voltage Peak value 200 V max Average value 100 V max Direct interelectrode capacitance approx triode unit Grid to plate 1 8 pF Grid to cathode heater and pentode elements 2 8 pF Plate to cathode heater and pentode element...

Page 181: ...age to be used When a voltage dropping resistor is used the minimum value of resistor that will assure tube operation within the boundary of the curve can be determined by the relation Where Pentode grid 1 to triode plate 0 2 pF max Pentode plate to triode plate 0 1 pF max Class A1 Amplifier Maximum Ratings Design Maximum Values Triode Unit Pentode Unit Plate voltage 330 V 330 V Grid 2 screen grid...

Page 182: ...onnected together within the tube Grid 2 input expressed as a percentage of maximum grid 2 input rating 100 80 50 40 20 0 20 40 60 80 100 120 Grid 2 voltage expressed as a percentage of maximum grid 2 supply voltage rating Area of permissible operation Figure 10 2 Grid 2 screen grid input rating curve Plate volts Plate volts Type 6973 grid 1 0 V with E variable c2 Type 6973 grid 2 250 V with E var...

Page 183: ...onnected to Output Transformer Tap Design Maximum Values Plate and grid 2 supply voltage 410V Plate dissipation 12 W Grid 2 input 1 75 W Envelope temperature at hottest point 250ºC Typical Operation with Fixed Bias values are for two tubes Plate supply voltage 375 V Grid 2 screen grid supply voltage Note 1 Grid 1 control grid voltage 33 V Peak AF grid 1 to grid 1 voltage 67 V Zero signal cathode c...

Page 184: ... having moderate dc requirements The pin layout is shown in Figure 10 5 This tube like other power handling devices should be adequately ventilated Typical rating chart is shown in Figure 10 6 Selected tube parameters are listed in Table 10 6 5 Figure 10 5 Terminal pinout of the 6CA4 Figure 10 6 6CA4 rating chart ...

Page 185: ...ximum capacitance for capacitor input to filter 50 μF Minimum inductance for choke input to filter 1 H Typical Operation with Capacitor Input to Filter AC plate to plate supply voltage 700 V rms Filter input capacitor 50 μF Total effective plate supply impedance per plate 240 Ω Average output current 150 mA DC output voltage at input to filter approx at 150 mA load current 347 V Typical Operation ...

Page 186: ... all parts and labor There are a few limitations which are detailed below 1 Because vacuum tubes have a limited lifetime the warranty covers tubes for the first 2 years following shipment 2 WhitakerAudio will pay shipping if needed for covered repair for the first year of ownership Thereafter the owner pays shipping both ways if needed for repair 3 The warranty is void if unauthorized repairs are ...

Page 187: ...m tubes which normally run hot Do not touch these devices as serious burns may result Other components may normally run hot notably the power transformer 3 This product is intended for private consumer audio applications It is not rated for commercial industrial or public venues 4 Do not remove the bottom access panel as dangerous voltages are present 5 This product is intended for operation at 11...

Page 188: ...20 W Stereo Integrated Amplifier WhitakerAudio 20 W Stereo Integrated Audio Amplifier ...

Page 189: ...assis components Parts are organized by component number and device type For example all 1 kΩ 1 2 watt resistors for the transistorized preamplifier PWB are packaged together Each group of parts is placed in a resealable clasp type envelope with a self adhesive label applied Labels such as Avery 5260 are useful for this purpose Recommended envelopes include the following 2 25 inch by 3 5 inch enve...

Page 190: ...plifier PWB 1 right D51 Rectifier 2 A 1 kV Amplifier PWB 1 right R11 R12 1 kΩ 0 5 W 1 Amplifier PWB 1 right Quick disconnect terminal posts quantity 58 Amplifier PWB 1 right VR51 Power thermistor 10 Ω cold Amplifier PWB 1 right R13 8 2 kΩ 0 5 W Amplifier PWB 1 right Heater circuit wire 5 ft 22 green brown solid Amplifier PWB 1 right Printed Wiring Board Speaker Terminals PWB Amplifier PWB 1 right ...

Page 191: ...10 μF 100 V electrolytic Amplifier PWB 2 left R26 R27 100 kΩ 0 5 W 1 Amplifier PWB 2 left inch threaded 4 standoff quantity 10 Amplifier PWB 2 left C61 100 μF 100 V electrolytic Amplifier PWB 2 left R28 R29 1 kΩ 0 5 W 1 Amplifier PWB 2 left RYL2 5 V dc relay contacts 240 V ac 30 A SPDT Amplifier PWB 2 left C63 C64 1 000 μF 25 V electrolytic Amplifier PWB 2 left R30 8 2 kΩ 0 5W Amplifier PWB 2 left...

Page 192: ...6 R128 R138 R158 R165 1 kΩ 0 5 W Preamplifier Module Daughterboard PWB Preamplifier Module C111 C119 0 047 μF 50 V polyester Preamplifier Module R107 R117 30 kΩ 0 5 W Preamplifier Module 2 terminal Molex housing header quantity 2 Preamplifier Module C112 C120 0 0022 μF 100 V polyester Preamplifier Module R108 R118 470 kΩ 0 5 W Preamplifier Module 4 terminal Molex housing heading quantity 4 Preampl...

Page 193: ...Ω 0 5 W Power Management Module Q201 Q202 2N494 2N491 NTE6400A Power Management Module C202 1000 pF 100 V Power Management Module R202 15 mΩ 0 5 W Power Management Module Q203 Q206 C9F NTE5408 Power Management Module C203 0 047 μF 100 V Power Management Module R203 R206 R212 150 Ω 0 5 W Power Management Module Q204 2N406 NTE102A Power Management Module C204 C205 1 000 μF 50 V electrolytic Power Ma...

Page 194: ... 13 Power Management Module SW203 High temp thermostat Power Management Module R217 180 kΩ 0 5 W Power Management Module F201 0 5 A slo blow fuse and fuse holder Power Management Module Press on heatsink quantity 2 Power Management Module Table 4 Chassis Component Labels T1 Output transformer Primary 6600 Ω plate to plate 20 W Secondary 4 8 16 Ω R55 100 Ω 2W potentiometer Chassis Components J1 J10...

Page 195: ... hardware Chassis Components Handle side quantity 2 Chassis Components PL51 115 V ac pilot lamp Chassis Components Back panel overlay Chassis Components Front panel handles quantity 2 Chassis Components Cable clamp hardware Chassis Components Top Chassis Components decal Chassis Components Power cord Chassis Components Plexiglas trim Chassis Components Hookup wire Chassis Components AC power conne...

Page 196: ...196 WhitakerAudio ...

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