DYNAKIT STEREO 70 has been designed to meet the
needs of the discriminating listener for a moderate -power, high performance amplifier. The power rating of the Stereo 70 is suitable for use with all modern loudspeaker systems including the low efficiency types. The quality of the Stereo 70 is unequalled by other designs, and the components used are of the finest type so that the quality of the amplifier will be maintained through many years of use. The use of prewired printed circuitry makes it possible to offer this unit in kit form, so that even an inexperienced constructor can build the amplifier and be assured of excellent performance. Average construction time is about five hours, and detailed step by step instructions and pictorial diagrams permit construction without any prior knowledge of electronic kit assembly. The Stereo 70 can be used for both stereophonic and monophonic sound reproduction. It.contains two independent power amplifiers capable of 35 watts of continuous power on each channel. A convenient front panel switch permits parallelling the inputs for 70 watts of power in monophonic use. The high power capability and low internal impedance of the amplifiers provide excellent damping for all types of high quality speaker systems without need to make adjustments to match specific speaker installations.
All elements of the Stereo 70 are conservatively designed and rated. Each amplifier uses the new 7199 driver tube and push pull EL-34/6CA7 tubes operated well below maximum ratings. The new Dynaco A-470 output transformer has been especially designed to provide 0 p tim u m operation in this circuit. Absolute stability of operation is obtained under all conditions of operation,. and the patented Dynaco circuit is pre-assembled on a heavy duty printed circuit board which is supplied with all critical parts mounted and soldered in place. The Stereo 70 is guaranteed for a full year of use - a unique testimonial to the qualityof the parts used and the conservativeness of their operation. The listening quality of the Stereo 70 is comparable to that of the world famous Mark II and Mark III Dynakits. Musical l' e pro d u c t it 0 n is effortless, with naturalness and clarity. The bass is firm and perfectly defined. The high frequencies are smooth, without harshness, and with accurate delineation of the most minute orchestral nuance. Whether in stereophonic or monophonic use, the Stereo 70 performs with unequalled listening pleasure.

D Y N A COl N C.

617 NORTH

FORTY.FIRS;~'STREET,

PHILADELPHIA 4, PA.
SPECIFICATIONS Power Output: 35 watts continuous; 80 watts peak each channel Frequency Response: 0.5 db from 10 cps to 40 KC Power Response: 20 cps to 20 KC without ex c e e din g 1% distortion within 1 db of 35 watts 1M Distortion: Less than 1% at 35 watts Hum and Noise: Inaudible; better than 90 db below 35 watts Sensitivity: 1.3 volts rms input for 35 watts output Output Impedances: 4, 8 and 16 ohms Damping Factor: 15 Minimum Channel Separation: 55 db Tube Complement: EL-34 (4), 7199 (2), GZ-34, selenium rectifier Finish: Bright nickel chassis, vinyl coated charcoal brown cover Power Consumption: 175 watts Size: 13" x 9 1/2" x 6 1/2" ShIPPing Weight: 32 pounds Special Features: matched tubes, dual Dyna Biasets for noncritical adjustment, provision for powering two preamps , without interaction, fuse post, stereo-mono switch, on-off switch Price Including Protective Cover: $99.95 (West Coast $104.95)

For Use with the

DYNAKIT STEREO 70

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Dynakit Stereo ContrOl, DSC-1 - a fl e xi b I e stereo adaptor which adds convenience to the stereophonic system. Includes exclusive "Blend" control for eliminating the hole-in-the-middle effect. $12.95 Dynakit Stereo Panel Mount, PM-2S - single front panel and convenient m 0 u n tin g brackets for simple, handsome mounting of a Dynakit stereo center. $5.95 Dynakit Cabinet Set, CM-2S - a front plate and walnut table -top cabinet com bin a t ion for the Dynakit stereo center. $17.95

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Dynakit Preamplifiers,- th~ finest units'made. Simple, flexible. Easily assembled, with distortionless performance. One for monophonic use or a pair for stereophonic application. $34.95 each

SERIAL NUMBER

6701028
This number must be mentioned in all communications concerning Dynakit.
MONO S TfREO DYNAKIT STEREO 70

B L A RIGHT. SE

()'rNA COMPANY

PREAMP

('ltCUII_Y
P""ILA-,. 'A MAor IN U. S A "AnNlEP

Price $1.00

PAT. NOS. 2815407 and 2815408

SPECIFICATIONS

Power Output Frequency Response Power Response Inte rmodulation Distortion Hum and Noise Sensitivity Output Impedances Damping Factor Minimum Channel Separation Power Consumption Preamp Provision
35 watts continuous, 80 watts peak each channel
.5 db from 10 cps to 40 kc
20 cps to 20 kc within 1 db of 35 watts at less than 1% distortion Less than 1% at 35 watts (normally about.5%). Less than.05% at 1 watt Inaudible; better than 90 db below rated power 1.3 volts rms input for 35 watts out 4, 8, 16 ohms each channel db 190 watts 50/60 cps Two power takeoffs with independent heater windings to eliminate interaction. Each 6.3 volts 1 amp, 350 volts dc 10 mao Dynakit preamplifiers plug in directly without modification. EL-34 (4), 7199 (2), GZ-34/5AR4, selenium rectifier. 13" by 9-1/2" by 6-1/2" high 32 pounds Chassis and bottom plate bright nickel plated. charcoal brown vinyl paint. Cover finished in
Tube Complement Size Weight Finish

-l:! 6 '70

DESCRIPTION
INSTRUCTIONS FOR ASSEMBLING THE DYNAKIT STEREO 70
An internal capacitive feedback loop balances the phase inverter at the highest frequencies, and the a r ran gem e n t provides accurately balanced driving signals to the output tubes. These tubes are type EL-34's (one pair for each channel) operating well below their maximum ratings. The output tubes use a fixed bias arrangement which is set through use of Dyna Biaset (pat pending) which provides optimum linearity of the tubes and minimizes the effects of unbalanced components. The connection of the output tubes includes a small percentage of screen loading which improves the regulation of the output stage and makes it corr-paratively uncritical of load impedance.
Your Dynakit stereo 70 is a complete dual 35 watt power amplifier kit which offers the highest possible fidelity, at low cost and in a compact arrangement. It uses a patented circuit of outstanding performance characteristics, along with top quality parts, including the new Dynaco SuperFidelity A-470 transformers --the finest available. The measured specifications show that the stereo 70 is an amplifier of unequalled performance, and its lis ten in g quality is also unrivalled by any regardless of price. This amplifier has characteristics and power rating ideal for either stereophonic or monophonic use. The two non-interacting 35 watt channels provide adequate power, in a stereophonic or two channel system, for loudspeakers of any level of efficiency. The channels can be paralleled for a full 70 watts of low distortion output, suitable for practically any monophonic use even where several loudspeakers are in use in different areas. The high power capability and low internal impedance provide excellent damping for all types of high quality speaker systems without need to make adjustments to match specific speaker installations. The design features of your Dynakit which contribute to its superior listening quality include some which are not revealed by the customary steadystate laboratory measurements. For example, the stereo 70 does not exhibit bounce and flutter when pulsed with a transient signal. Thus a sharp percussive signal like a drum beat or a piano note will be reproduced with sharpness and clarity and neit~er overhang nor muddiness. The Stereo 70, unhke many other amplifier circuits, has been designed to provide its specified performance on a loudspeaker load, not just under laboratory measuring conditions. Therefore, the connection of a loudspeaker to the amplifier does not deteriorate its performance or listening quality. In addition, due to the high quality of the output transformers used, the Dynakit's power handling capabilities are maintained over the entire audio band without the sharp rise in distortion which characterizes most amplifiers at the extremes of high and low frequencies. The Stereo 70 uses a circuit arrangement based on that of the Dynakits Mark n and Mark III which has become world famous as one of superior quality while essentially simple and trouble -free. The new 7199 tube is used as a pentode high gain voltage amplifier directly coupled to a cathodyne phase inverter. All parameters are adjusted for minimum distortion. This type of phase inverter has the unique advantage that its operation is independent of tube aging so that no adjustments are required in maintaining optimum performance.
The imp e dan c e match and bias conditions utilized in the output stage provide minimum distortion over a very wide dynamic range. In addition, 20 db of negative voltage feedback lowers the distortion to an unmeasurable proportion at normal listening levels and to less than 1% intermodulation distortion at 35 watts output on each channel. The use of a minimum number of phaseshifting stages along with car e f u I transformer design makes it practical to have unconditional stability at both high and low frequencies. This feature of the design means that there is no tendency toward motorboating or oscillation under any condition of use. The inherent lin e a I' it Y of the circuit, the complete stability, and the prefabrication of all critical wiring on the printed circuit assembly make construction completely non-critical. The use of conservatively 0 per ate d, highest quality components insures superior and de pen dab I e operation over a long period of time. GENERAL WIRING PRACTICE Assembly of the Dynakit stereo 70 is quite simple compared to general kit assembly requirements. This is true because all critical parts of the Dynakit are factory assembled for you on the printed circuit assembly. Other parts are put out in the open through a free and uncluttered layout so there is easy accessibility for wiring or trouble shooting purposes. Construction of your Dynakit should not take more than about five hours because of these simplifications. Upon opening your kit, check the components with the parts list. Familiarize yourself with the components; they can be identified by comparison with the pictorial diagram and by specified color coding. Proper color coding will be mentioned for each resistor as it is used. Tools r e qui l' e d for easy assembly of your Dynakit are soldering iron (small tip) or soldering

gun, long nose pliers, screwdriver, and wire cutters. Although not essential, a low cost wire stripper and cutter of the type which can be purchased for less than $1.00 will greatly facilitate cutting and stripping the various leads in the kit. Good soldering technique is valuable in obtaining sat i s f act 0 I' Y results from any electronic equipment. ALL SOLDERING MUST BE DONE WITH ROSIN CORE SOLDER. There is no warranty on any equipment in which acid core solder has been used. Make sure that the solder used is plainly marked "Rosin Core." If you have solder on hand the origin of which is doubtful it is wise to obtain new 50/50 or 60/40 l' a sin core solder. Whenever sol del' in g is required, the assembly instructions specify it by "(S)." If this symbol is not shown aiter a connection is specified, it indicates that further connections will be made at that point before soldering. Soldering is accomplished by heating the joint with the iron until solder is hot enough to flow when touched to the joint. It is not desirable to feed the solder to the iron. It should be fed to the junction of iron and joint. After the solder flows, the iron should be held in place for a few seconds and removed when it is seen that the solder has contacted both parts of the connection - the lug and the wire to which it is connected. It should not show a ball of solder but a smooth transition from solder to component lead. Before a p ply in g solder the joint should be clean and the lead should be crimped in place so as to have mechanical security. It is not necessary to wrap leads around contacts many times. A single turn and pinching together with long nose pliers is suitable. After soldering, there should be no play at the joint if the lead is wiggled with a pair of plie rs. It is practical to do all soldering with a pencil type iron of low wattage rating. A small tip is extremely useful when working in a confined space. If a solder ing gun is used, it should be used with discretion since the amount of heat available is far more than l' e qui red for soldering light wires. Component leads should be trimmed as they are used; the length should be such that the proper connection can be made from point to point without strain on lugs or components. Care should be exercised not to allow wires to touch one another unless they are actually connected to the same point. The ins t I' U c t ion s which follow have been arranged for simplified procedure in which the work can be done without interference between the various portions of the wiring. It is recommended that the instructions be followed on a step by step basis, checking off each stage as it is completed. The pictorial diagrams should be used for refer-

ence and all connections checked against these before going on to the next stage. If the wiring is done methodically and each step checked carefully, your amplifier should work without difficulty as soon as it is completed.
MECHANICAL ASSEMBLY PICTORIAL DIAGRAMS SHOULD BE CONSULTED DURING ALL PHASES OF ASSEMBLY 1 ("I) Mount the seven octal sockets with 4/40 hardware (the smallest screws supplied). Note that there is a small slot or keyway in the center hole of each socket; be sure in each instance that this keyway is properly oriented as shown in the pictorial diagram. Insert screws from the top of the chassis and mount the sockets from the bottom. Fasten with nuts and lockwashers. 2
Place the bakelite insulator over the front of the two socket input connector and mount the combination from the inside of the chassis using 4/40 hardware.
3 (II) Mount the SPDT slide switch (with three lugs) next to the input connector. No nuts or lockwashers are necessary since this item has threaded holes. 4 (.;) Mount the two four screw terminal strips on the c has sis rear from the outside. Fasten with 4/40 hardware. 5 (v') Mount the two 10,000 ohm potentiometers in the 3/8" holes near the center of the chassis. Locate with the three connecting lugs facing the front of th,: chassis. Put a 3/8" lockwasher on each shaft, insert from the inside, and fasten with a 3/8" nut. 6
Fasten the long 4/40 screw between the two potentiometers with a 4/40 nut. Then place the selenium rectifier over the screw. The lug marked (+) should be closest to the chassis and both lugs should face the rear of the chassis. Fasten with 4/40 lockwasher and nut.
7 (J) Mount the rubber grommet in the 3/8" hole in the cente l' of the rear fl a n g e of the chassis. 8 (/). Mount the fuse post in the D shaped hole in the rear of the chassis. The rubber washer goes between the chassis outside and the shoulder of the fuse post. Fa s ten with special nut provided.
9 (L1 Mount the SPST on-off switch (two lugs) on the chassis rear. The con nee tin g lugs should be located as shown in the pictorial diagram. No lockwashers or nuts are necessary. 10 (.y-Mount the power transformer, PA-060, in the large center cutout. The wires should face the front of the chassis. Fasten the two mounting screws at the rear with #8 lockwashers and nuts. Place a cable clamp over each of the two front mounting screws and fasten loosely with 118 lockwashers and nuts. The green, red, and white pairs of wires should be threaded through the left cable c I amp as should the green -yellow and brown-yellow ones. Pass the brown pair through the right clamp.
11 ( ) Mount the choke, C-354, on the right side
WIRING PROCEDURE EACH LENGTH OF HOOKUP WIRE SPECIFIED SHOULD HAVE APPROXIMATELY 1/4" OF INSULATION STRIPPED FROM EACH END UNLESS OTHERWISE SP ECIFIED.

I (V[ Connect the red-black transformer lead to the lower (+) lug of the selenium rectifier (S). 2 (
'1 Twist the pair of white leads and dress
them from the power transformer to socket VI. Connect one lead to pin #2 of VI (S). Connect the other white lead to pin #8 of VI.
3 ('-) Twist the red pair of leads and dress them to socket VI. Connect one red lead to pin #4 of VI (S). Connect the other red lead to pin #6 of VI (S). 4 (?1 Twist the pair of green leads together and dress to socket V2. Connect one green lead to pin 1/2 of V2. Connect the other green lead to pin #7 of V2.
below the c has sis. Put the #8 screws through the chassis from the top and fasten underneath with lockwashers and nuts. The leads should face the front of the chassis. 12
(-1 Us ing 4/40 hardware, mount the seven lug
terminal strip on the left side opposite the choke, following the pos ition shown in the pictorial diagram.

('/1' Twist

the brown pair and dress them to socket V7. Connect one brown lead to pin #2 of V7. Connect the other brown lead to pin #7 of V7.
13 (---) Mount both A-470 output transformers with #8 hardware. Note that the shorter leads come through the holes in the rear.
14 U) Mount the quadruple section filter capacitor in the special cutout. Fasten by twisting each mounting tab one -quarter turn. Note that the four connecting lugs are identified by markings at the base of the lugs. Be sure to orient the capacitor properly, with the lugs positioned as in the pictorial.
6 ( '1' Dress the brown -yellow and green -yellow leads a I' 0 un d to the s even lug terminal strip. Connect the brown -yellow to lug #7 and the green-yellow to lug #5. 7 8
Connect the red -yellow lead to the solder lug near the filter capacitor. the red lead from the left 0 u t put transformer through both cable clamps and the red lead from the right output transformer through the right clamp. Connect both red leads to filter capacitor lug #1. (The lead from the right output transformer can be trimmed to the required length).

(-1 Feed

Mount two solder lugs with a #4 screw and nut next to the quad filter capacitor. This is the main grounding point of the entire amplifier and should be tightened securely with the two lugs pointing as shown in the pictorial. MOST TRANSFORMER LEADS ARE PRE-CUT TO THE PROPER LENGT HS AND DO NOT REQUIRE CUTTING. HOWEVER, THEY CAN BE SHORTENED WHERE DESIRED. IT IS ESSENTIAL THAT THEY NOT BE CUT TOO SHORT FOR CONNECTIONS WHEN THE LEADS ARE POSITIONED IN A C COR DAN C E WITH THE PICTORIAL DIAGRAM. IN THE EVENT THAT THE TRANSFORMERS ARE RETURNED TO THE FACTORY FOR REPLACEMENT OR INSPECTION, THE LE ADS ,MUST BE OF U SAB LE LENGT H OR THE WARRANTY WILL BE VOIDED.

9 ('/) Feed the two choke leads through the right cable clamp, con n e c t one lead to filter capacitor lug #2 and the other lead to lug 4{ 1. (These leads can be trimmed as reqUired). Tighten the two nuts holding the cable clamps. 10 (v') Dress the power transformer black leads around the end bell and connect one lead to lug A of the fuse post (S). Connect other black lead to lug #l of on -off switch (S). 11 ('1 Connect the short black lead from the right output transformer to lug #4 of the 4 screw terminal strip. Connect the brown lead to lug #3 (S). Connect the orange lead to lug #2 (S). Connect the yellow lead to lug # 1.
Repeat step 11 for the left output transformer and the left screw terminal strip. Twist the blue and green leads from the left output transformer together and connect the green lead to pin #4 of V3. Connect the blue lead to pin #3 of V3 (8). Twist bluewhite and green-white together and connect the blue-white lead to pin #3 of V2 (8). Connect the green-white lead to pin #4 of V2 (8).
(v{ Connect the negative end of the other 50
MFD capacitor to lug #3 of the 7 lug strip and the positive end to lug #1.
Cut both leads of another 10,000 ohm (brownblack-orange) resistor to 1". Connect one end to lug #2 of the seven lug strip. Connect the other end to lug It 1 of the strip (8). Connect one end of a 6" wire to lug #6 of the 7 lug strip (8). Connect the other end to the ground lug near the filter capacitor. See pictorial.
14 (v) Repeat step 13 for right output transformer. The blue lead is twisted with the green and goes to pin #3 of V6 (8), green to pin #4, while the blue-white and green-white, after twisting together, are connected to pins #3 (8) and #4 (8) of V7.
26 (t.r Connect one end of a 6" wire to lug -# 3 of the 7 lug strip~,(S). Connect the other end to lug of the left bias potentiometer.
27 ("1 Connect one end of a 6" wire to lug #4 of the 7 lug strip (8). Connect the other end to the negative (top) lug of the selenium rectifie l' (8).
Connect the center (common) lead of the double (2 x.02) disc capacitor to lug #6 of the 7 lug terminal strip. Connect one of the outside wires to lug #5 of the strip (8) and the other outside wire to lug #7 of the strip (8). Twist together a pair of 6" wires except for 1-1/2" at each end. Connect one end of one wire to pin #2 of V7 (8). Connect the other wire to pin #7 of V7 (8). Connect one of the other ends to pin #2 of V6. Connect the remaining end to pin #7 of V6.

28 (0' Connect one end of an 8" wire to lug #2 of the 7 lug strip (8). Connect the other end to lug #3 of the left bias control.
29 (V'j Connect one end of a 3" wire to lug #3 of the right side bias potentiometer (8). Connect the other end to lug # 3 of the left side bias potentiometer (8).
17 (p1f Twist together a pair of 7" wires except for 1-1/2" at each end. Connect one end of one wire to pin #2 of V6 (8). Connect the other wire to pin # 7 of V6 (8). Dres s the pair to the front panel of the chassis and over tothe right power takeoff socket. Connect one end of the pair to pin #1 of the takeoff socket. Connect the other of the twisted pair to pin #2 of the takeoff socket.
30 ("1 Connect one end of a 3" wire to lug It 1 of the right s ide bias potentiometer (8). Connect the other end to lug # 1 of the left side potentiometer (8).

(t1"

Connect one end of a 5-1/4" wire to lug #8 of VI (8). Connect the othe r end to lug # 2 of the quad filter capacitor (8).
32 ("'1 T rim the leads of a 6800 ohm (blue -grayred) resistor to 1". Connect one lead to lug # 1 of the filter capacitor (8). Connect the othe l' end to lug #4 of the filter capac itor. 33
18 (v1 Repeat step 16 for connection of V2 and V3.
19 (VJ Repeat step 17 for connection of V3 to left power takeoff socket.
(.-1 Connect one end of a 15.6 ohm res istor to
the ground lug on base of V2 socket (8). Connect the other end to pin #8 of V2.
20 (.q' Connect one end of a 5" wire to lug # 1 of the 7 lug strip. Connect the other end to lug #6. 21 (0 Connect the negative end (-) of a 50 MFD capacitor to lug #4 of the seven lug strip. Connect the positive (+) capacitor lead to lug #1. 22
Strip both ends of a 5" wire 1/2". Feed one end through pin # 1 of V2 (8) and connect it to pin #8 of V2 (8). Feed the other end through pin H8 of V3 (8) and connect to pin 411 of V3.
35 (0 Connect one end of a 4 -1/2" wire to pin # 1 of V3 (8). Connect the othe l' end to pin # 8 of the left power takeoff socket (8). 36

(t:1"

Cut both leads of a 10,000 ohm (brown-blackorange) res istor to 1". Connect one end of the resistor to lug #4 of the 7 lug strip and the other end to lug #3.
Connect one end of the othe l' 15.6 ohm resistor to the ground lug at the base of socket V7 (8). Connect the other end to pin #1 of V7.
Strip both ends of a 5" wire 1/2". Feed one end through pin #8 (8) and connect it to pin #1 of V7 (8). Feed the other end through pin #1 (8) of V6 and connect to pin #8 of V6.

("1

Connect a 3-1/2" wire from eyelet #20 (8) to capacitor lug #4 (8). Observe two wires extending from the printed circuit board just under the input socket. Connect the extended wire on the right to the ground (short) lug of the right input socket. Con n e c t the left extended wire to the ground (short) lug of the left input socket.
38 (v) Connect one end of a 4-1/2" wire to pin #8 of V6 (8). Connect the other end to pin #8 of the right power takeoff socket (8). 39 (I/j Connect one end of a 1000 ohm (brownblack-red) resistor to pin #5 of V2 (8). Connect the other end to pin #6. Repeat for V3, V6 and V7. Keep the resistor pigtails short (about 1/2") for all four of these resistors. 40
47 (V) Connect a 1-1/2" wire from eyelet #18 (8) to lug #5 of the right power takeoff socket
Mount the printed circuit board PC -3 from the bottom of the chassis. Note the numbers of the eyelets are upright when looking from the rear of the chassis. Use a 4/40 screw, lockwasher and nut at each mounting hole. The two wires from the board s h a u I d be straightened carefully. These are used at a later step.
In making solder connections to the printed
48 (0 Twist together a pair of 3-1/4" Connect one pair of ends to eyelets and #16 (8). Connect the other ends #1 (8) and #2 (8) of the right power socket.
wires. # 15 (8) to pins takeoff
49 (v') Connect one end of a 10 ohm (brown-blackblack) resistor from eyelet #10 (8) to pin #3 of the right power takeoff socket (8). 50 ("1 Connect one end of a 2-1/2" wire to eyelet # 21 (8). Connect the other end to lug # 2 of the right potentiometer (8). 51 ('"1 Connect one end of a 5-1/2" wire to eyelet #14 (8), and connect the other end to pin #4 of V6 (8). 52 (0 Connect a 2" wire from lug #3 of the input switch (8) to the long lug of the right input socket. 53 ({/) Connect one end of a 470,000 ohm (yellowviolet-yellow) resistor to long lug of right input socket. Connect the other end to the ground (short) lug of the right input socket
circuit board, all connections are made to the numbered eyelets in the board. In this way, there is no danger of damaging the printed wiring or the components which are part of the board as sembly. These eyelets already have solder in them and it is very easy to make sol de r connections to the board. The lead wires should have their ends stripped back about 1/4", and these stripped ends should be tinned by heating with a soldering iron and touching against the solder. When the wire is to be soldered to the eyelet on the board, the eyelet is heated until the solder flows; and then the wire end is pushed into the eyelet and held in place until the solder sets. This type of soldering can be done with a very small iron, and it is preferable not to use any more heat on the eyelet on the board than is required to get the solder to flow. 41 (~Connect a 2-3/4" wire from eyelet #23 (8) of the printed circuit board to pin #6 of V6

Connect one end of a 470,000 ohm (yellowviolet-yellow) resistor to lug # 1 of the input switch (8). Connect the other end to the ground short lug of the left input socket (8).
55 (0 Connect one end of a 1-3/4" wire to eyelet # 17 (8). Connect the other end to the long lug of the right input socket (8). 56
Connect a 3" wire from eyelet U22 (8) to pin tl6 of V7 (8). Connect a 3" wire from eyelet #19 (8) to filter capacitor lug # 3.
Connect one end of a 3-1/2" wire to eyelet #7 (8). Connect the other end to the long lug of the left input socket.
44 (tI) Cut the leads of a 22,000 ohm (red-redorange) res isto!' to 1". Connect one end of the resistor to capacitor lug' #3 (8). Connect the other end to capacitor lug 114.
57 (0 Connect a short link of wire from the left input socket long lug (8) to lug 4i 2 of the input switch (8). 58
Connect a 1-1/4" wire from eye let # 3 (8) to pin 115 of the left takeoff socket (8).
59 (t/f" Con n e c t one end of a 10 ohm, (brownblack-black), I' e sis tor to eyelet #8 (8). Connect the other end to pin #3 of the left power takeoff socket (8). 60 (,;/) Twist a pair of 3-1/2" wires together and connect one pair of ends to eyelets #4 (8) and # 5 (8). Connect the other pair of ends to pins #1 (8) and #2 (8) of the left power takeoff socket.
the line cord to the knot then strip about 1/2" of insulation from each end. Connect one end to lug B of the fuse post (S). Conneet the othe I' end to lug # 2 of the on -off switch (S). This completes the wiring of your amplifier.
It is wise to go back and check all connec-
61 (vj Connect one end of a 2-1/2" wire to eyelet #2 (8), Connect the other end to pin #6 of V3 (S).
62 (0 Connect one end of a 3-1/2" wire from eyelet #1 (S). Connect the other end to pin #6 of V2 (8). 63 (I/) Connect one end of a 2-1/2" wire to eyelet # 6 (S). Connect the othe I' end to lug # 2 of the left potentiometer (S).
64 (V) Connect one end of an 8" wire to pin #4 of V3 (8). Connect the other end to eyelet # 11 (8). It is important to keep this wire close to the chassis and carried around the printed c i r cui t board, as shown in the pictorial.
tions for correctness and for good soldering. All hardware should also be checked for tightness. The fuse can now be installed in the fuse post on the rear of the chassis. The four rubber feet should then be pushed into the four holes in the bottom plate - from outside tow a I' d inside and seated with a twisting motion. INITIAL ADJUSTMENT Plug in the EL-34 tubes V2, V3, V6 and V7. Also plug the 7199 tubes into pI' in ted circuit sockets. Do not plug in GZ-34 rectifier tube. If an 0 h m met e I' is available, measure resistance from capacitor lug #2 to ground. This should be in excess of one hundred thousand ohms. Inspect wiring to make sure that all joints are soldered and that no parts are shorting together. Plug line cord into 117 volt ac line and turn on switch. While tubes are warming up, set the bias adjusting potentiometers to the c en tel' of their rotation. This is approximately the correct setting and can serve as an emergency operating adjustment if no test instruments a I' e available. (H 0 WE V E R, OPERATION WITHOUT CORRECT BIAS ADJUSTMENT 18 NOT RECOMMENDED A8 IT RE8ULT8 IN POOR PERFORMANCE AND PROBABLE DAMAGE TO COMPONENTS.) Your D y n a kit includes Dyna Biaset (patent pending) which greatly simplifies setting of the bias voltage. This can now be done with the most simple and inexpensive types of dc meters as long as they have a rating of 1000 ohms per volt or higher. The correct setting of the bias provides a total cathode current for each pair of EL-34 tubes of 100 mao This current through the precision 15.6 ohm resistors produces a voltage drop of exactly 1. 56 volts dc, and this v 0 It age can be checked at pin #8 of each preamplifier power takeoff socket. 1. 56 volts is also the voltage which is furnished by a "0" type flashlight dry cell. Thus any fresh cell of this type can be used for an accurate reference standard for bias setting. The procedure for setting the bias is to measure the voltage output of a "D" type dry cell and note the meter reading. Then insert the positive meter probe in the pin #8 hole of the left preamplifier power socket (note that outside the chassis the pin n u m bel's are counted counterclockwise from the keyway while inside the chassis they are counted clockwise). The negative met e r probe

If a three terminal magnetic cartridge arrangement is used, it is very possible that hum will be encountered if the equipment from the two channels has any additional interchannel connection (beside the common shield from the pickup). Connection of the Stereo 70 should not give this trouble. However, dissimilar units in each channel can be a source of hum when three terminal cartridges are used. Crystal and ceramic cartridges which go into high level inputs should not normally introduce this type of hum problem.
tively far from the s pea k e I' s, this problem is diminished, and' optimum results are obtainable for several listening positions simultaneously. The most basic consideration of the installation and use of a stereophonic system is that stereo alone does not create realism and high quality sound. Two low grade stereo channels will not give the qua 1it Y of one high grade monophonic channel. There is no substitute for high quality components, carefully installed. IN CASE OF TROUBLE Your Dynakit Stereo 70 has been designed to be as free from trouble as possible. However, a mistake in assembly or a defective component can affect its performance or m a k e it inoperative. Some trouble-shooting procedures are suggested in case difficulty is encountered. Naturally the wiring should be checked very carefully to make sure that all con nee t ion s have been made in accordance with instructions. The tubes should light after a few seconds of warmup. If they do not, it is probable that there is no ac voltage getting into the amplifier, which indicates a possible blown fuse. Fuse failure
If fuses blow frequently without apparent cause, this may sometimes be rectified by using a slow blow type of fuse. However, do not exceed the 3 ampere fuse rating when replacing fuses.
If fuses blow within 30 seconds of turning the amplifier on, remove the GZ -34 rectifier tube and see if this cures the problem. If it does, the rectifier may be bad and another should be tried. A 5U4GB type of rectifier can be substituted for trial purposes, although using this tube type will cut down the maximum power rating of the amplifieI'. If the GZ -34 is not at fault, the quadruple section filter capacitor may be snorted. Generally, shorts in this section of the amplifier will show up in a measurement of resistance (with the amplifier unplugged from the 117 volt line) from capacitor to ground. This resistance should exceed 100,000 ohms.

Positioning of loudspeakers will af fee t the quality of stereophonic reproduction. Generally, moderate distances of six to ten feet along the same wall pro vi d e the best effect. If greater spacing is required, the use of a blend control can help to provide "fill" in the middle. However, if extreme distance is required, a "phantom" middle channel is useful. It has generally been established that an L + R combination of the two channels provides the best center fill. Information on the proper method for obtaining this signal, using either the two regular stereo amplifiers, or a third amplifieI', may be obtained on request from Dynaco, Inc. This arrangement will also provide a combined signal for a remote monophonic extension speaker. In most rooms, the proper balance of the stereo system will be different for different listening positions. If the listening positions are rela-
Fuses blowing with all tubes removed indicate either m i s wi l' in g or a defective P A-060 power transformer. Tubes glowing
If one (or a pair) of the EL-34's glows a bright red color after slight warmup, it is possible that the tube is bad, or there may be a fault in the bias supply which supplies neg at i v e voltage to the EL-34' s, measurable (with a high impedance meter such as a VTVM) at pin #5 of each EL-34. The
actual value of negative voltage will depend on the setting of the respective bias potentiometer. With the Biaset con n e c t ion reading the proper 1.56 volts, the negative voltage at the EL-34 tubes should be within 20% of minus 32 volts. If the two tubes in a pair have different negative voltages at pin #5, as measured by a VTVM, this is a clue to a defective component or wiring. (V2 and V3 make one pair; V6 and V7 make the other pair). A small difference in voltage indicates either a runaway tube (which can be checked by borrowing the pair from the other channel) or a leaking.1 mfd capacitor on the PC-3 board. If one tube has no negative voltage, it indicates that there is an open connection from the bias supply to this tube.
If no meter is available, it is possible to pin down the fault with a glowing tube by switching the two tubes of the pair. In the same socket exhibits the glow, the fault is in the amplifier bias supply or components. If the same tube glows in transposed position, it is most like~a defective tube.
eluded in these instructions. Departures of more than 10% from the values shown indicate possible malfunctioning of some of the circuit components. Hum and noise
If excessive hum or noise appear, it is necessary to determine whether they occur within the amplifier. Sometimes noise in the preamplifier is blamed on the amplifier. The simple test is to remOve the cables from the input socket and see whether the same noise is present. If the noise is removed when the cable is unplugged, it is in the preceding equipment which should then be checked. If not, it is probably in the amplifier.

It is advisable to remove the input cable and see whether insertion of the plug makes a "thump" through the loudspeaker. Sometimes, a defective cable or pre amp prevents signal from coming through while the amplifier itself is operative. If there is no signal from the preamplifier, but a "thump" can be induced by unplugging the shielded cable from the preamplifier or by inserting the tip of a small screwdriver into the input socket, then the fault is not in the amplifier but in the associated equipment.
If a meter is available, voltages should be checked in comparison with the voltage table in-
which are standard dealer items can be purchased from most electronic supply stores.
If transformers are returned for factory repair or exchange, they should be removed from the equipment without cutting the leads short. If leads have been cut rather than unsoldered, so that they are no longer usable, the guarantee on the transformer is voided.
CORRESPONDENCE, PARTS RETURN, OR KITS RETURNED FOR FACTORY SERVICE. It is the factory prerogative to limit the service facility to one year from date of purchase. When shipping the amplifier for service, a note must be attached specifying the symptoms, the name and address of the sender, and the serial number of the unit. The kit should be securely packed with stuffing inside the cover to prevent the tubes from falling out of the sockets. It should be placed in a rugged carton surrounded by several inches of shredded paper or other soft packing material. The original carton is not suitable for shipp ing a wired amplifier. Shipment should be made by prepaid Railway Express, where possible; and repaired kits will be returned by Railway Express COD for freight and service charges unless these charges have been prepaid. Parcel post is not a safe method for shipment of completed kits and should not be used. Dyna Company assumes no responsibility or liability for dam age s or injuries sustained in assembly or operation of the Dynakit.
In the event that the assembled kit does not function properly or breaks down after some use, Dyna Company will service the kit for a service fee of $7.50 plus the cost of parts which have been damaged by the user or are past the guarantee period. This service facility is not available for kits which are incompletely wired, or have been wired with other than rosin core solder, or in which changes or modifications have been made without fa c tor y authorization. In addition, NO PARTS WILL BE REPLACED NOR WILL ANY SERVICE BE AVAILABLE FOR KITS WHERE THE GUARANTEE POST CARD HAS NOT BEEN RETURNED. THE SERIAL NUMBER ON THIS INSTRUCTION BOOK MUST BE MENTIONED IN

STEREO 70 PARTS LIST (Parts of similar type which do not change performance may sometimes be included as a matter of expediency). Chassis set (including cover and bottom plate) Power Transformer - PA-060 Output Transformers - A-470 Choke - C-354 Output Tubes - EL-34 Rectifier Tube - GZ -34 Driver Tubes - 7199 Octal sockets Printed Circuit Assembly - PC-3 Filter Capacitor - Quad @ 525V Capacitors - 50 MFD Dual Ceramic Capacitor - 2 x.02 MFD Selenium Rectifier Four Screw Terminal Strips Fuse Post plus rubber washer and mounting nut Fuse - 3A Sio-Blo Line Cord On-Off Switch (SPST) Input Switch (SPDT) Dual Input Socket Input Socket Insulator Potentiometers 10,000 ohm Seven Lug Terminal Strip ~ Hank Wire RESISTORS 15.6 ohms 1000 ohms (brown-black-red) 10,000 ohms (brown-black-orange) 470,000 ohms (yellow-violet-yellow) 10 ohms (brown-black-black) 6800 ohms (blue-grey-red) 22,000 ohms (red-red-orange) Rubber Feet 4/40 x 1/4" Screws 4/40 Nuts #4 Lockwashers 4/40 x 3/4" Screw #6 Sheet Metal Screws 8/32 Screws 8/32 Nuts #8 Lockwashers Rubber Grommet Solder Lugs 3/8 Lockwashers 3/8 Nuts Cable Clamps Set Instructions & Pictorials
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SPECIAL INSTRUCTIONS FOR OPTIONAL 120.240 VOLT POWER TRANSFORMERS

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*Measurements at these points vary from tube to tube and do not indicate wbether performance is normal. HMeasurements at these points can only be made with a vacuum tube voltmeter. The two tubes in a pair should have identical readings. Capacitor A B '" C. D lug Selenium rectifier Bottom (+) lug 50 ac Top (-) lug -65 dc Printed circuit Eyelets #3 and #volts dc
Stereo 70s supplied with power transformer PA-521 may be connected for either 120 volt or 240 volt AC operation as follows: For 120 Volt Operation 1 ( ) Twist together the black and black-white leads, and connect both to lug A of the fuse post (5). 2 Twist together the violet and violet-white leads, and connect both to lug #1 of the on-off switch (5). For 240 Volt Operation 1 ( ) Connect the black lead to lug A of the fuse post (S). 2 ( ) Connect the violet lead to lug #1 of the on-ofT switch (5). 3 ( ) Twist together the violet-white and the black-white leads, and solder them together. Insulate this connection with electrical tape. When connected for 240 volt operation, a 1 ~ ampere slow blow fuse should be used.