SERIAL NUMBER

6701028

This number must be men­tioned in all communica­tions concerning Dynakit.

INPUTDYNAKIT STEREO 70

LEFT OJ LEFT RIGHT

MONO I ~mQS TfREO •

PAT. NOS. 2815407 and 2815408

BLASE.RIGHT

1. H v... ~

PREAMP POWER

()'rNA COMPANYP""ILA-,. 'AMAor IN U. S A('ltCUII_Y "AnNlEP

Price $1.00

Power Output

Frequency Response

Power Response

Inte rmodulation Distortion

Hum and Noise

Sensitivity

Output Impedances

Damping Factor

Minimum Channel Separation

Power Consumption

Preamp Provision

Tube Complement

Size

Weight

Finish

SPECIFICATIONS

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

15

55 db

190 watts 50/60 cps

Two power takeoffs with independent heater windings to eliminateinteraction. 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. Cover finished incharcoal brown vinyl paint.

-l:! 6 '70 70~~

INSTRUCTIONS FOR ASSEMBLING THE DYNAKIT STEREO 70

DESCRIPTION

Your Dynakit stereo 70 is a complete dual 35watt power amplifier kit which offers the highestpossible fidelity, at low cost and in a compactarrangement. It uses a patented circuit of out­standing performance characteristics, along withtop quality parts, including the new Dynaco Super­Fidelity A-470 transformers --the finest available.The measured specifications show that the stereo70 is an amplifier of unequalled performance, andits lis ten in g quality is also unrivalled by anyregardless of price.

This amplifier has characteristics and powerrating ideal for either stereophonic or monophonicuse. The two non-interacting 35 watt channelsprovide adequate power, in a stereophonic or twochannel system, for loudspeakers of any level ofefficiency. The channels can be paralleled for afull 70 watts of low distortion output, suitable forpractically any monophonic use even whereseveral loudspeakers are in use in different areas.The high power capability and low internal imped­ance provide excellent damping for all types ofhigh quality speaker systems without need to makeadjustments to match specific speaker installations.

The design features of your Dynakit which con­tribute to its superior listening quality include somewhich are not revealed by the customary steady­state laboratory measurements. For example, thestereo 70 does not exhibit bounce and flutter whenpulsed with a transient signal. Thus a sharp per­cussive signal like a drum beat or a piano note willbe reproduced with sharpness and clarity and neit~er

overhang nor muddiness. The Stereo 70, unhkemany other amplifier circuits, has been designed toprovide its specified performance on a loudspeakerload, not just under laboratory measuring condi­tions. Therefore, the connection of a loudspeakerto the amplifier does not deteriorate its perform­ance or listening quality. In addition, due to thehigh quality of the output transformers used, theDynakit's power handling capabilities are maintain­ed over the entire audio band without the sharp risein distortion which characterizes most amplifiersat the extremes of high and low frequencies.

The Stereo 70 uses a circuit arrangement basedon that of the Dynakits Mark n and Mark III whichhas become world famous as one of superior qual­ity while essentially simple and trouble -free. Thenew 7199 tube is used as a pentode high gain voltageamplifier directly coupled to a cathodyne phaseinverter. All parameters are adjusted for minimumdistortion. This type of phase inverter has theunique advantage that its operation is independentof tube aging so that no adjustments are requiredin maintaining optimum performance.

An internal capacitive feedback loop balancesthe phase inverter at the highest frequencies, andthe a r ran gem e n t provides accurately balanceddriving signals to the output tubes. These tubesare type EL-34's (one pair for each channel) oper­ating well below their maximum ratings. The out­put tubes use a fixed bias arrangement which isset through use of Dyna Biaset (pat pending) whichprovides optimum linearity of the tubes and mini­mizes the effects of unbalanced components. Theconnection of the output tubes includes a smallpercentage of screen loading which improves theregulation of the output stage and makes it corr-­paratively uncritical of load impedance.

The imp e dan c e match and bias conditionsutilized in the output stage provide minimum dis­tortion over a very wide dynamic range. In addi­tion, 20 db of negative voltage feedback lowers thedistortion to an unmeasurable proportion at normallistening levels and to less than 1% intermodulationdistortion at 35 watts output on each channel.

The use of a minimum number of phase­shifting stages along with car e f u I transformerdesign makes it practical to have unconditionalstability at both high and low frequencies. Thisfeature of the design means that there is no tend­ency toward motorboating or oscillation under anycondition of use.

The inherent lin e a I' it Y of the circuit, thecomplete stability, and the prefabrication of allcritical wiring on the printed circuit assemblymake construction completely non-critical. Theuse of conservatively 0 per ate d, highest qualitycomponents insures superior and de pen dab I eoperation over a long period of time.

GENERAL WIRING PRACTICE

Assembly of the Dynakit stereo 70 is quitesimple compared to general kit assembly require­ments. This is true because all critical parts ofthe Dynakit are factory assembled for you on theprinted circuit assembly. Other parts are put outin the open through a free and uncluttered layoutso there is easy accessibility for wiring or troubleshooting purposes. Construction of your Dynakitshould not take more than about five hours becauseof these simplifications.

Upon opening your kit, check the componentswith the parts list. Familiarize yourself with thecomponents; they can be identified by comparisonwith the pictorial diagram and by specified colorcoding. Proper color coding will be mentioned foreach resistor as it is used.

Tools r e qui l' e d for easy assembly of yourDynakit are soldering iron (small tip) or soldering

1

gun, long nose pliers, screwdriver, and wirecutters. Although not essential, a low cost wirestripper and cutter of the type which can be pur­chased for less than $1.00 will greatly facilitatecutting 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 electronicequipment. ALL SOLDERING MUST BE DONEWITH ROSIN CORE SOLDER. There is no war­ranty on any equipment in which acid core solderhas been used. Make sure that the solder used isplainly marked "Rosin Core." If you have solderon hand the origin of which is doubtful it is wise toobtain new 50/50 or 60/40 l' a sin core solder.Whenever soldel' in g is required, the assemblyinstructions specify it by "(S)." If this symbol isnot shown aiter a connection is specified, it indi­cates that further connections will be made at thatpoint before soldering.

Soldering is accomplished by heating the jointwith the iron until solder is hot enough to flowwhen touched to the joint. It is not desirable tofeed the solder to the iron. It should be fed to thejunction of iron and joint. After the solder flows,the iron should be held in place for a few secondsand removed when it is seen that the solder hascontacted both parts of the connection - the lug andthe wire to which it is connected. It should notshow a ball of solder but a smooth transition fromsolder to component lead.

Before a p ply in g solder the joint should beclean and the lead should be crimped in place soas to have mechanical security. It is not neces­sary to wrap leads around contacts many times. Asingle turn and pinching together with long nosepliers is suitable. After soldering, there shouldbe no play at the joint if the lead is wiggled with apair of plie rs. It is practical to do all solderingwith a pencil type iron of low wattage rating. Asmall tip is extremely useful when working in aconfined space. If a solder ing gun is used, itshould be used with discretion since the amount ofheat available is far more than l' e qui red forsoldering light wires.

Component leads should be trimmed as theyare used; the length should be such that the properconnection can be made from point to point withoutstrain on lugs or components. Care should beexercised not to allow wires to touch one anotherunless they are actually connected to the samepoint.

The ins t I' U c t ion s which follow have beenarranged for simplified procedure in which thework can be done without interference between thevarious portions of the wiring. It is recommendedthat the instructions be followed on a step by stepbasis, checking off each stage as it is completed.The pictorial diagrams should be used for refer-

2

ence and all connections checked against thesebefore going on to the next stage. If the wiring isdone methodically and each step checked carefully,your amplifier should work without difficulty assoon as it is completed.

MECHANICAL ASSEMBLY

PICTORIAL DIAGRAMS SHOULD BE CONSULTEDDURING ALL PHASES OF ASSEMBLY

1 ("I) Mount the seven octal sockets with 4/40hardware (the smallest screws supplied).Note that there is a small slot or keyway inthe center hole of each socket; be sure ineach instance that this keyway is properlyoriented as shown in the pictorial diagram.Insert screws from the top of the chassisand mount the sockets from the bottom.Fasten with nuts and lockwashers.

2 (0 Place the bakelite insulator over the frontof the two socket input connector and mountthe combination from the inside of thechassis using 4/40 hardware.

3 (II) Mount the SPDT slide switch (with threelugs) next to the input connector. No nutsor lockwashers are necessary since thisitem has threaded holes.

4 (.;) Mount the two four screw terminal stripson the c has sis rear from the outside.Fasten with 4/40 hardware.

5 (v') Mount the two 10,000 ohm potentiometersin the 3/8" holes near the center of thechassis. Locate with the three connectinglugs facing the front of th,: chassis. Put a3/8" lockwasher on each shaft, insert fromthe inside, and fasten with a 3/8" nut.

6 (0 Fasten the long 4/40 screw between the twopotentiometers with a 4/40 nut. Then placethe selenium rectifier over the screw. Thelug marked (+) should be closest to thechassis and both lugs should face the rearof the chassis. Fasten with 4/40 lock­washer and nut.

7 (J) Mount the rubber grommet in the 3/8" holein the cente l' of the rear fl a n g e of thechassis.

8 (/). Mount the fuse post in the D shaped hole inthe rear of the chassis. The rubber washergoes between the chassis outside and theshoulder of the fuse post. Fa s ten withspecial nut provided.

9 (L1 Mount the SPST on-off switch (two lugs) onthe chassis rear. The con nee tin g lugsshould be located as shown in the pictorialdiagram. No lockwashers or nuts arenecessary.

WIRING PROCEDURE

EACH LENGTH OF HOOKUP WIRE SPECIFIEDSHOULD HAVE APPROXIMATELY 1/4" OFINSULATION STRIPPED FROM EACH ENDUNLESS OTHERWISE SP ECIFIED.

13 (---) Mount both A-470 output transformers with#8 hardware. Note that the shorter leadscome through the holes in the rear.

12 (-1 Us ing 4/40 hardware, mount the seven lugterminal strip on the left side opposite thechoke, following the pos ition shown in thepictorial diagram.

11 () Mount the choke, C-354, on the right sidebelow the c has sis. Put the #8 screwsthrough the chassis from the top and fastenunderneath with lockwashers and nuts. Theleads should face the front of the chassis.

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I (V[ Connect the red-black transformer lead tothe lower (+) lug of the selenium rectifier(S) .

2 ( '1 Twist the pair of white leads and dressthem from the power transformer to socketVI. 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 themto socket VI. Connect one red lead to pin#4 of VI (S). Connect the other red lead topin #6 of VI (S).

4 (?1 Twist the pair of green leads together anddress to socket V2. Connect one greenlead to pin 1/2 of V2. Connect the othergreen lead to pin #7 of V2.

5 ('/1' Twist the brown pair and dress them tosocket V7. Connect one brown lead to pin#2 of V7. Connect the other brown lead topin #7 of V7.

6 ( '1' Dress the brown -yellow and green -yellowleads a I' 0 un d to the s even lug terminalstrip. Connect the brown -yellow to lug #7and the green-yellow to lug #5.

7 (1.-1 Connect the red -yellow lead to the solderlug near the filter capacitor.

8 (-1 Feed the red lead from the left 0 u t puttransformer through both cable clamps andthe red lead from the right output trans­former through the right clamp. Connectboth red leads to filter capacitor lug #1.(The lead from the right output transformercan be trimmed to the required length).

9 ('/) Feed the two choke leads through the rightcable clamp, con n e c t one lead to filtercapacitor lug #2 and the other lead to lug4{ 1. (These leads can be trimmed as re­qUired). Tighten the two nuts holding thecable clamps.

10 (v') Dress the power transformer black leadsaround the end bell and connect one lead tolug A of the fuse post (S). Connect otherblack lead to lug #l of on -off switch (S).

11 ('1 Connect the short black lead from the rightoutput transformer to lug #4 of the 4 screwterminal strip. Connect the brown lead tolug #3 (S). Connect the orange lead to lug#2 (S). Connect the yellow lead to lug # 1.

Mount the quadruple section filter capacitorin the special cutout. Fasten by twistingeach mounting tab one -quarter turn. Notethat the four connecting lugs are identifiedby markings at the base of the lugs. Besure to orient the capacitor properly, withthe lugs positioned as in the pictorial.

Mount two solder lugs with a #4 screw andnut next to the quad filter capacitor. Thisis the main grounding point of the entireamplifier and should be tightened securelywith the two lugs pointing as shown in thepictorial.

10 (...y-Mount the power transformer, PA-060, inthe large center cutout. The wires shouldface the front of the chassis. Fasten thetwo mounting screws at the rear with #8lockwashers and nuts. Place a cable clampover each of the two front mounting screwsand fasten loosely with 118 lockwashers andnuts. The green, red, and white pairs ofwires should be threaded through the leftcable c I amp as should the green -yellowand brown-yellow ones. Pass the brownpair through the right clamp.

14 U)

MOST TRANSFORMER LEADS ARE PRE-CUTTO THE PROPER LENGT HS AND DO NOTREQUIRE CUTTING. HOWEVER, THEY CAN BESHORTENED WHERE DESIRED. IT IS ESSEN­TIAL THAT THEY NOT BE CUT TOO SHORTFOR CONNECTIONS WHEN THE LEADS AREPOSITIONED IN A C COR DAN C E WITH THEPICTORIAL DIAGRAM. IN THE EVENT THATTHE TRANSFORMERS ARE RETURNED TO THEFACTORY FOR REPLACEMENT OR INSPEC­TION, THE LE ADS ,MUST BE OF U SAB LELENGT H OR THE WARRANTY WILL BEVOIDED.

12 ('1 Repeat step 11 for the left output trans­former and the left screw terminal strip.

23 (v{ Connect the negative end of the other 50MFD capacitor to lug #3 of the 7 lug stripand the positive end to lug #1.

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18 (v1 Repeat step 16 for connection of V2 and V3.

19 (VJ Repeat step 17 for connection of V3 to leftpower takeoff socket.

14 (v) Repeat step 13 for right output transformer.The blue lead is twisted with the green andgoes to pin #3 of V6 (8), green to pin #4,while the blue-white and green-white, aftertwisting together, are connected to pins #3(8) and #4 (8) of V7.

32 ("'1 T rim the leads of a 6800 ohm (blue -gray­red) resistor to 1". Connect one lead tolug #1 of the filter capacitor (8). Connectthe othe l' end to lug #4 of the filter capac itor.

30 ("1 Connect one end of a 3" wire to lug It 1 ofthe right s ide bias potentiometer (8). Con­nect the other end to lug # 1 of the left sidepotentiometer (8).

31 (t1" Connect one end of a 5-1/4" wire to lug #8of VI (8). Connect the othe r end to lug #2of the quad filter capacitor (8).

24 (0' Cut both leads of another 10,000 ohm (brown­black-orange) resistor to 1". Connect oneend to lug #2 of the seven lug strip. Connectthe other end to lug It 1 of the strip (8).

25 0' Connect one end of a 6" wire to lug #6 ofthe 7 lug strip (8). Connect the other endto the ground lug near the filter capacitor.See pictorial.

26 (t..r Connect one end of a 6" wire to lug -# 3 ofthe 7 lug strip~,(S). Connect the other endto lug 11 1 of the left bias potentiometer.

27 ("1 Connect one end of a 6" wire to lug #4 ofthe 7 lug strip (8). Connect the other endto the negative (top) lug of the seleniumrectifie l' (8).

29 (V'j Connect one end of a 3" wire to lug #3 ofthe right side bias potentiometer (8). Con­nect the other end to lug #3 of the left sidebias potentiometer (8).

28 (0' Connect one end of an 8" wire to lug #2 ofthe 7 lug strip (8). Connect the other endto lug #3 of the left bias control.

33 (.-1 Connect one end of a 15.6 ohm res istor tothe ground lug on base of V2 socket (8).Connect the other end to pin #8 of V2.

34 (VI Strip both ends of a 5" wire 1/2". Feedone end through pin #1 of V2 (8) and connectit to pin #·8 of V2 (8). Feed the other endthrough pin H8 of V3 (8) and connect to pin411 of V3.

35 (0 Connect one end of a 4-1/2" wire to pin #1of V3 (8). Connect the othe l' end to pin # 8of the left power takeoff socket (8).

36 M Connect one end of the othe l' 15.6 ohmresistor to the ground lug at the base ofsocket V7 (8). Connect the other end topin #1 of V7.

Twist together a pair of 6" wires exceptfor 1-1/2" at each end. Connect one end ofone wire to pin #2 of V7 (8). Connect theother wire to pin #7 of V7 (8). Connect oneof the other ends to pin #2 of V6. Connectthe remaining end to pin #7 of V6.

Twist together a pair of 7" wires except for1-1/2" at each end. Connect one end of onewire to pin #2 of V6 (8). Connect the otherwire to pin #7 of V6 (8). Dres s the pair tothe front panel of the chassis and over totheright power takeoff socket. Connect one endof the pair to pin #1 of the takeoff socket.Connect the other of the twisted pair to pin#2 of the takeoff socket.

20 (.q' Connect one end of a 5" wire to lug # 1 ofthe 7 lug strip. Connect the other end tolug #6.

21 (0 Connect the negative end (-) of a 50 MFDcapacitor to lug #4 of the seven lug strip.Connect the positive (+) capacitor lead tolug #1.

22 (t:1" Cut both leads of a 10,000 ohm (brown-black­orange) res istor to 1". Connect one end ofthe resistor to lug #4 of the 7 lug strip andthe other end to lug #3.

13 (-7 Twist the blue and green leads from the leftoutput transformer together and connect thegreen lead to pin #4 of V3. Connect theblue lead to pin #3 of V3 (8). Twist blue­white and green-white together and connectthe blue-white lead to pin #3 of V2 (8).Connect the green-white lead to pin #4 ofV2 (8).

17 (p1f

16 (0

15 (ur Connect the center (common) lead of thedouble (2 x .02) disc capacitor to lug #6 ofthe 7 lug terminal strip. Connect one ofthe outside wires to lug #5 of the strip (8)and the other outside wire to lug #7 of thestrip (8).

37 (-1 Strip both ends of a 5" wire 1/2". Feedone end through pin #8 (8) and connect it topin #1 of V7 (8). Feed the other endthrough pin #1 (8) of V6 and connect to pin#8 of V6.

38 (v) Connect one end of a 4-1/2" wire to pin #8of V6 (8). Connect the other end to pin #8of 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 forV3, V6 and V7. Keep the resistor pigtailsshort (about 1/2") for all four of theseresistors.

40 (0{ Mount the printed circuit board PC -3 fromthe bottom of the chassis. Note the num­bers of the eyelets are upright when look­ing from the rear of the chassis. Use a4/40 screw, lockwasher and nut at eachmounting hole. The two wires from theboard s h a u I d be straightened carefully.These are used at a later step.

In making solder connections to the printedcircuit board, all connections are made tothe numbered eyelets in the board. In thisway, there is no danger of damaging theprinted wiring or the components which arepart of the board as sembly. These eyeletsalready have solder in them and it is veryeasy to make sol de r connections to theboard. The lead wires should have theirends stripped back about 1/4", and thesestripped ends should be tinned by heatingwith a soldering iron and touching againstthe solder. When the wire is to be solderedto the eyelet on the board, the eyelet isheated until the solder flows; and then thewire end is pushed into the eyelet and heldin place until the solder sets. This type ofsoldering can be done with a very smalliron, and it is preferable not to use anymore heat on the eyelet on the board thanis 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(8) .

42 ('-1 Connect a 3" wire from eyelet U22 (8) topin tl6 of V7 (8).

43 (0 Connect a 3" wire from eyelet #19 (8) tofilter capacitor lug #3.

44 (tI) Cut the leads of a 22,000 ohm (red-red­orange) res isto!' to 1". Connect one end ofthe resistor to capacitor lug' #3 (8). Con­nect the other end to capacitor lug 114.

45 (0 Connect a 3-1/2" wire from eyelet #20 (8)to capacitor lug #4 (8).

46 ("1 Observe two wires extending from theprinted circuit board just under the inputsocket. Connect the extended wire on theright to the ground (short) lug of the rightinput socket. Con n e c t the left extendedwire to the ground (short) lug of the leftinput socket.

47 (V) Connect a 1-1/2" wire from eyelet #18 (8)to lug #5 of the right power takeoff socket(8) .

48 (0 Twist together a pair of 3-1/4" wires.Connect one pair of ends to eyelets #15 (8)and #16 (8). Connect the other ends to pins#1 (8) and #2 (8) of the right power takeoffsocket.

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 ofthe 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 #4of V6 (8).

52 (0 Connect a 2" wire from lug #3 of the inputswitch (8) to the long lug of the right inputsocket.

53 ({/) Connect one end of a 470,000 ohm (yellow­violet-yellow) resistor to long lug of rightinput socket. Connect the other end to theground (short) lug of the right input socket(8) .

54 (£11 Connect one end of a 470,000 ohm (yellow­violet-yellow) resistor to lug #1 of the inputswitch (8). Connect the other end to theground 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 longlug of the right input socket (8).

56 (/.-1 Connect one end of a 3-1/2" wire to eyelet#7 (8). Connect the other end to the longlug of the left input socket.

57 (0 Connect a short link of wire from the leftinput socket long lug (8) to lug 4i 2 of theinput switch (8).

58 (0 Connect a 1-1/4" wire from eye let # 3 (8) topin 115 of the left takeoff socket (8).

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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 leftpower takeoff socket (8).

60 (,;/) Twist a pair of 3-1/2" wires together andconnect one pair of ends to eyelets #4 (8)and # 5 (8). Connect the other pair of endsto pins #1 (8) and #2 (8) of the left powertakeoff socket.

61 (vj Connect one end of a 2-1/2" wire to eyelet#2 (8), Connect the other end to pin #6 ofV3 (S).

62 (0 Connect one end of a 3-1/2" wire fromeyelet #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 ofthe left potentiometer (S).

64 (V) Connect one end of an 8" wire to pin #4 ofV3 (8). Connect the other end to eyelet#11 (8). It is important to keep this wireclose to the chassis and carried around theprinted c i r cui t board, as shown in thepictorial.

65 (0 Connect one end of a 5" wire to eyelet #9(8). Connect the other end to solder lugnear filter capacitor.

66 (r/) Connect one end of a 12" wire to lug # 1 ofthe left screw terminal strip (S). Connectthe other end to eyelet #12 (S). Seepictorial.

67 ("1 Connect one end of a 10-1/2" wire to lug#4 (S) of the- teft screw terminal strip.Connect the""'other end to the solder lugnear filter capacitor.

68 «(.)) Connect one end of a 9 -1/2" wire to lug #1of the right screw term ina 1 strip (S).Connect the other end to eyelet # 13 (8). Seepictorial.

69 (e-j Connect one end of a 9" wire to lug #4 (8)of the right screw terminal strip. Connectthe other end to solder lug near capacitor.

70 (v) Connect short link of wire from capacitorground lug (8) to solder lug near capacitor.Solder all six wires which go to the pair ofsolder lugs.

71 ( ) Insert the line cord through the grommet inthe rear of the chassis. Pull through aboutfive inches, tie a knot and then pull fromthe outside till the knot is a g a ins t thegrommet. Separate the two conductors of

6

the line cord to the knot then strip about1/2" of insulation from each end. Connectone end to lug B of the fuse post (S). Con­neet the othe I' end to lug # 2 of the on -offswitch (S). This completes the wiring ofyour amplifier.

It is wise to go back and check all connec­tions for correctness and for good solder­ing. All hardware should also be checkedfor tightness. The fuse can now be in­stalled in the fuse post on the rear of thechassis. The four rubber feet should thenbe pushed into the four holes in the bottomplate - from outside tow a I' d inside andseated 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 circuitsockets. Do not plug in GZ-34 rectifier tube. Ifan 0 h m met e I' is available, measure resistancefrom capacitor lug #2 to ground. This should bein excess of one hundred thousand ohms. Inspectwiring to make sure that all joints are solderedand that no parts are shorting together. Plug linecord into 117 volt ac line and turn on switch.While tubes are warming up, set the bias adjustingpotentiometers to the c en tel' of their rotation.This is approximately the correct setting and canserve as an emergency operating adjustment if notest instruments a I' e available. (H 0 WE V E R,OPERATION WITHOUT CORRECT BIAS ADJUST­MENT 18 NOT RECOMMENDED A8 IT RE8ULT8IN POOR PERFORMANCE AND PROBABLEDAMAGE TO COMPONENTS.)

Your D y n a kit includes Dyna Biaset (patentpending) which greatly simplifies setting of thebias voltage. This can now be done with the mostsimple and inexpensive types of dc meters as longas they have a rating of 1000 ohms per volt orhigher. The correct setting of the bias provides atotal cathode current for each pair of EL-34 tubesof 100 mao This current through the precision15.6 ohm resistors produces a voltage drop ofexactly 1. 56 volts dc, and this v 0 It age can bechecked at pin #8 of each preamplifier power take­off socket. 1. 56 volts is also the voltage which isfurnished by a "0" type flashlight dry cell .. Thusany fresh cell of this type can be used for anaccurate reference standard for bias setting.

The procedure for setting the bias is to meas­ure the voltage output of a "D" type dry cell andnote the meter reading. Then insert the positivemeter probe in the pin #8 hole of the left pream­plifier power socket (note that outside the chassisthe pin n u m bel's are counted counterclockwisefrom the keyway while inside the chassis they arecounted clockwise). The negative met e r probe

should touch the c has sis. P lug in the GZ -34rectifier tube, and in about 10 seconds there willbe a current flow which will cause a meter deflec­tion. As the rectifier warms up, the reading willincrease. The left bias potentiometer should beadjusted until the meter reading at pin #8 is thesame as across the dry cen (this reading will be1. 56 volts if the meter is of sufficient accuracy).This adjustment should then be made using theright bias potentiometer and measuring the voltageat pin 118 of the right power takeoff socket. Thenrepeat the setting for the left control and left setof tubes. There may be Some drifting of the read­ing as the tubes heat, but this will stabilize within15 minutes after which no further adjustment isrequired. Small variations will occur with linevoltage changes. These will have no effect onperformance. A It h au g h the setting is a semi­permanent one, at times of tube replacement orsimilar repair or maintenance work, resetti.ng ofthe bias will preserve peak performance and keepdistortion at an absolute minimum.

If in the course of bias setting it is found thatthe control range of the potentiometer is insuffi­cient to obtain the correct setting, do not operatethe amplifier until the cause of the difficulty hasbeen established. Operation with incorrect biascan lead to damage to the output tubes and/or othercomponents.

Note that the use of pin #8 as directed in thewiring instructions means that this pin cannot beused as a connection point for preamplifiers if thepreamplifiers take power from the power takeoffsockets of the front panel. Most preamplifiers donot require the use of this pin. However, for thosewhich do, some other pin must be used as a biascheck point. If no other pin is available, theconnection from pins 1/8 of V3 and V6 to the pre­amplifier power sockets must be omitted; and biasmeasurements should be based on voltages readdirectly at pin #8 of V2 or V3 for the left channelor pin 1i8 of V6 or V7 for the right channel.

PREAMPLIFIERS

The Dynakit Stereo 70 can be used with anyconventional stereo or monophonic preamplifier,or pair of monophonic preamplifiers. Preamp­lifiers which con t a i n their own built-in powersupply can be used by connecting their audio cablesto the input socket. Those units which requirepower from the amplifier can be readily used withthe Dynakit provided that the power sockets on thefront panel of the Dynakit are properly wired. Thepreceding instructions include the proper wiringfor both Dynakit and Heathkit WA-P2 preamplifiersso that these can be inserted without modification.Should others requiring different socket connec­lions be used, the socket wiring can be changed tosuit their requirements.

PROTECTIVE COVER

The protective cover which is supplied with theStereo 70 has been designed to be both functionaland good looking. It should be used on the amplifierif the amplifier is located where it can be inadver­tently to u c h e d by anybody. There is voltageappearing above chassis on the printed circuitboard which is not lethal, but which can give anuncomfortable shock. In addition, the tubes gethot in normal operation, and touching them canresult in a minor burn. Therefore, the protectivecover should generally be used.

The amplifier should be located where there isadequate ventilation - at least one foot of spaceabove it and a few inches all around. The amplifiercan be located away from other elements of thehigh fidelity system so there should be no need toput it in too confined a space. NEVER put anythingon top of the cover which can obstruct air flow.Always use the amplifier with the tubes in verticalposition.

The cover and bottom plate arc affixed at thesame time. The amplifier chassis should be setover the bottom plate, the cover lowered over thechassis, and then the three pieces are fastenedtogether with the six sheet metal sc rews throughthe chassis sides.

USING THE STEREO 70

The Dynakit Stereo 70 is designed to be used inany of three different modes of operation: stereo­phonic use in which separate stereo channels arecarried through the two sides of the amplifier;high-low frequency amplification where one chan­nel carries the low frequencies and the other thehigh frequencies with a frequency dividing networkahead of the amplifier; and monophonic use withthe two channels paralleled so that 70 watts ofpower are available.

In stereo use, the stereo 70 provides 35 wattsper channel. A stereo preamplifier's two outputcables, or other left and right signals, are con­nected to the input jacks of the ste reo 70. Theinput switch is set to "stereo", and remains in thatpos ition whenever two input cables are connected,allowing the preamplifier to do all the switching.The right loudspeaker is connected to the "right"screw terminal strip between the "c" terminal andthe terminal corresponding to the speaker's im­pedance. The left loudspeaker is similarly con­nected to the "left" terminal strip.

If there are two monophonic preamplifierswhich require power from the amplifier, each isconnected to the respective preamplifier powertakeoff socket. As provided, these will accom-

7

modate Dynakit monophonic preamplifiers withoutmodification.

The stereo 70 can be turned on and off fromthe back panel switch, or this switch can be left in"on" position, and the amplifier switched from oneof the switched ac outlets on the associated pre­amplifier.

High-Low frequency amplification

For this type of operation the input switch onthe Stereo 70 should be put to "stereo" position.The low frequency output of the dividing or cross­over network should be fed to the left input, andthe "left" loudspeaker output should be connectedto the bass speaker. The high frequency output ofthe diViding or cross -over network should be fedthrough the right channel, and the tweeter con­nected to the "right" loudspeaker terminal strip.

Monophonic 70 watt amplification

For monophonic operation, the two channels ofthe Stereo 70 may be paralleled. For this, onlyone input cable is connected to either the left or theright input (but not both), the input s witch is set to"mono", and the outputs are connected together.An insulated wire jumper should be connected from"c" to "c" on the screw terminal strips. Anotherinsulated wire jumper should be connected from"8" to "8" if a 4 ohm loudspeaker is used, or from"16" to" 16" is an 8 ohm or 16 ohm loudspeaker isused. When using the 16 ohm loudspeaker in thisfashion, the amplifier's maximum power output isnot as great because of the impedance. mismatch,but there is no loss of power when using a 4 ohmor 8 ohm loudspeaker as specified above. Themaximum power available into a 16 ohm loudspeakeris still 55 watts, however, and there is a compen­sating factor. The distortion, as levels below max­imum, will be reduced by this type of connection.What happens is that the operating conditions areshifted from maximum power output to minimumdistortion. This same operation can also beachieved, of course, by connecting an 8 ohm loud­speaker to paralleled 8 ohm taps, or a 4 ohmloudspeaker to paralleled 4 ohm taps. Note thatwhenever the two outputs are paralleled, only oneinput cable should be used, the other input socketshould not be used, and the switch is on "mono".

It is also practical to use the "mono" positionwith a single input source with two separate loud­speakers. In this case, each speaker is connectedto one of the screw output strips using the imped­ance which pertains to the respective speaker. Nojumpers are required between the output strips.

A monophonic preamplifier wh i c h requirespower from the amp 1if ie r can be connected toeither of the two power takeoff sockets.

8

ENJOYING STEREOPHONIC SOUND

Stel' e 0 ph 0 n i c sound 0 if e r s an importantenhancement of enjoyment of your high fidelitysystem. The proper setup and use of your stereo­phonic system will bring considerable satisfaction.However, stereophony introduces problems in highfidelity reproduction which can dim in ish yourenjoyment of your hi fi system unless these prob­lems are understood and corrected. These fewnotes on the subject should assist materially in theinstallation and use of a stereophonic system whichadds to your listening pleasure.

The pieces of equipment to be used should beas similar as possible in each channel. This isparticularly true for the loudspeaker to be used.Different types and brands of speakers have verygreat differences in frequency response and otherimportant characteristics. If, for example, onespeaker has a peak in response at a certain fre­quency where the other does not, the stereophonicbalance will be changed at that frequency. Theneed for frequent rebalancing is due to this typeof dissimilarity.

There has been a relatively high proportion ofdissatisfaction with stereo which has arisen be­cause of the attempt to attach an inferior secondchannel to complete a system. If this channeldiffers from the first channel it frequently destroysany potential benefits of stereophonic sound.

The proper reproduction of monophonic discsthrough the stereo system requires the cancella­tion of identical signals (of opposite phase) so thatthere is no unwanted vertical signal component inthe output. This requires either the parallellingof the two sides of the cartridge or the parallellingof the outputs of identical preamps. If the preampsare slightly different, the vert i cal componentscannot be eliminated properly. In Dynakit pre­amplifiers, the critical components which deter­mine the response characteristics of the preamp­lifier playback characteristics have a toleranceof only 1% so that this pro b I e m cannot causedifficulty.

Channel phasing is a problem of stereo whichis readily solved, once understood. If, on a singlesound, one speaker cone moves inward while theother moves out, the s y s t em is not properlyphased, and the sound area between the speakerswill lack homogeneity. All tapes and all discs arenow reproduced so that their phasing is consistent.Therefore, once phasing of the playback equipmentis set it can be maintained for all tape and discsources without further change.

To check for proper phasing, playa monophonicrecording so that one signal comes through bothchannels. Then move back and forth between thespeakers. If phasing is correct, there will be a

smooth transition of sound between the speakers.If it is not correct, there will be an intermediatearea where the sound will shift -from one to theother. If phasing is not correct, it can be rectifiedby interchanging the two leads between one of theamplifier c h ann e I s and its associated speaker.There should be no need to change phasing oncethe system is set up properly.

Proper phasing of the stereo pickup or tapehead is generally accomplished by the manufac­turer of this item. However, this can be inverted ininstallation if directions are not followed precisely.If there is a drop in volume using a monophonictape or disc, this indicates probable incorrectphasing. An interchange of ground and "hot" sideof one of the cartridge channels or of the two leadsto one channel of the tape head will remedy thistype of incorrect phasing.

Hum is another problem which the stereo discplayback cartridge can introduce. In some cases(particularly where independent preamps are usedfor the two channels) the use of a common groundlead on the two inputs will provoke a hum condi­tion. For this reason, many stereo pickup manu­facturers provide separate ground connections foreach channel by using four cartridge terminals.The cable shields of the two channels should bekept separated.

If a three terminal magnetic cartridge arrange­ment is used, it is very possible that hum will beencountered if the equipment from the two channelshas any additional interchannel connection (besidethe common shield from the pickup). Connectionof the Stereo 70 should not give this trouble. How­ever, dissimilar units in each channel can be asource of hum when three terminal cartridges areused. Crystal and ceramic cartridges which gointo high level inputs should not normally introducethis type of hum problem.

Positioning of loudspeakers will af fee t thequality of stereophonic reproduction. Generally,moderate distances of six to ten feet along thesame wall pro vi d e the best effect. If greaterspacing is required, the use of a blend control canhelp to provide "fill" in the middle. However, ifextreme distance is required, a "phantom" middlechannel is useful. It has generally been establishedthat an L + R combination of the two channels pro­vides the best center fill. Information on the propermethod for obtaining this signal, using either thetwo 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 extensionspeaker.

In most rooms, the proper balance of thestereo system will be different for different listen­ing positions. If the listening positions are rela-

tively far from the s pea k e I' s, this problem isdiminished, and' optimum results are obtainablefor several listening positions simultaneously.

The most basic consideration of the installationand use of a stereophonic system is that stereoalone does not create realism and high qualitysound. Two low grade stereo channels will notgive the qua 1it Y of one high grade monophonicchannel. There is no substitute for high qualitycomponents, carefully installed.

IN CASE OF TROUBLE

Your Dynakit Stereo 70 has been designed to beas free from trouble as possible. However, amistake in assembly or a defective component canaffect its performance or m a k e it inoperative.Some trouble-shooting procedures are suggestedin case difficulty is encountered. Naturally thewiring should be checked very carefully to makesure that all con nee t ion s have been made inaccordance with instructions.

The tubes should light after a few seconds ofwarmup. If they do not, it is probable that thereis no ac voltage getting into the amplifier, whichindicates a possible blown fuse.

Fuse failure

If fuses blow frequently without apparent cause,this may sometimes be rectified by using a slowblow type of fuse. However, do not exceed the 3ampere fuse rating when replacing fuses.

If fuses blow within 30 seconds of turning theamplifier on, remove the GZ -34 rectifier tube andsee if this cures the problem. If it does, therectifier may be bad and another should be tried.A 5U4GB type of rectifier can be substituted fortrial purposes, although using this tube type willcut down the maximum power rating of the ampli­fieI'. If the GZ -34 is not at fault, the quadruplesection filter capacitor may be snorted. Generally,shorts in this section of the amplifier will show upin a measurement of resistance (with the amplifierunplugged from the 117 volt line) from capacitorto ground. This resistance should exceed 100,000ohms.

Fuses blowing with all tubes removed indicateeither m i s wi l' in g or a defective P A-060 powertransformer.

Tubes glowing

If one (or a pair) of the EL-34's glows a brightred color after slight warmup, it is possible thatthe tube is bad, or there may be a fault in the biassupply which supplies neg at i v e voltage to theEL-34' s, measurable (with a high impedance metersuch as a VTVM) at pin #5 of each EL-34. The

9

actual value of negative voltage will depend on thesetting of the respective bias potentiometer. Withthe Biaset con n e c t ion reading the proper 1.56volts, the negative voltage at the EL-34 tubesshould be within 20% of minus 32 volts. If the twotubes in a pair have different negative voltagesat pin #5, as measured by a VTVM, this is a clueto a defective component or wiring. (V2 and V3make one pair; V6 and V7 make the other pair).A small difference in voltage indicates either arunaway tube (which can be checked by borrowingthe pair from the other channel) or a leaking .1mfd capacitor on the PC-3 board. If one tube hasno negative voltage, it indicates that there is anopen connection from the bias supply to this tube.

If no meter is available, it is possible to pindown the fault with a glowing tube by switching thetwo tubes of the pair. In the same socket exhibitsthe glow, the fault is in the amplifier bias supplyor components. If the same tube glows in trans­posed position, it is most like~a defective tube.

The tubes sup P lie d with the Stereo 70 arematched and should be completely interchangeable.When making replacements of tubes, they shouldpreferably (although not absolutely essential) bereplaced in pairs which are matched. There isno need to maintain matching of all four EL-34tubes.

In emergencies, substitution of the tubes canbe made with at her tube types. The 5881 andKT -66 can be used in place of the EL-34's providedthe bias is readjusted to give 1.56 at the Biasetcheck point. The 5U4G or 5U4GB can be used inplace of the GZ -34. There is no substitute for the7199 tube.

No signal

If there is no signal coming through the ampli­fier, each side should be checked separately tosee whether one channel may be working. If oneworks, and the other does not, the working channelcan be used for test purposes. For example, thetubes can be interchanged to determine whetherthey will work in eithe r channel. In this way, adefective tube can be singled out.

It is advisable to remove the input cable andsee whether insertion of the plug makes a "thump"through the loudspeaker. Sometimes, a defectivecable or pre amp prevents signal from comingthrough while the amplifier itself is operative. Ifthere is no signal from the preamplifier, but a"thump" can be induced by unplugging the shieldedcable from the preamplifier or by inserting the tipof a small screwdriver into the input socket, thenthe fault is not in the amplifier but in the associatedequipment.

If a meter is available, voltages should bechecked in comparison with the voltage table in-

10

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eluded in these instructions. Departures of morethan 10% from the values shown indicate possiblemalfunctioning of some of the circuit components.

Hum and noise

If excessive hum or noise appear, it is neces­sary to determine whether they occur within theamplifier. Sometimes noise in the preamplifier isblamed on the amplifier. The simple test is toremOve the cables from the input socket and seewhether the same noise is present. If the noise isremoved when the cable is unplugged, it is in thepreceding equipment which should then be checked.If not, it is probably in the amplifier.

Compare the noise in the two channels. Ifboth are the same, it is not likely to be tubes likethe 7199 or EL-34 which affect only the channel inwhich they operate, but it could be the GZ-34 orthe quad capacitor or bias capacitors which arecommon to both sides of the circuit.

Sizzling sounds coming through the loudspeakermay come from poor can t act s between circuitelements and chassis. Make sure that groundconnections are tight.

In some rare cases, loud pops may be heardthrough the loudspeakers. These can come frompoor conditions inside the pins of the EL-34 tubes.Touching a hot soldering iron to these pins willrectify this. Make sure that solder is not depositedon the pin or the tube may not fit the socket.

In the event that trouble shooting will not cor­rect the problem, factory consultation is availablewithout charge, and factory service at moderatecharge.

FACTORY SERVICE AND GUARANTEE

The Dynakit Stereo 70 is designed to providegood service over a long period of time. It isintended to be used at the conventional 117 voltline input found in most homes. Operation up to125 volts will not cause any problem. Above thatvoltage, it is suggested that a voltage regulating oradjusting device be used in order to protect thecomponents in your amplifier. The normal guar­antee on the equipment is not applicable if it isused above the 125 volt rating.

All parts in the Stereo 70 are guaranteed for aperiod of one year from purchase except tubeswhich carry the standard EIA guarantee of 90 days.Parts which are defective will be replaced at nocharge if they are returned prepaid to the factoryeither directly or via the dealer from whom the kitis purchased. Many Dynaco dealers carry spareparts in stock to facilitate replacements. Afterthe guarantee period is past, Dynaco will supplyany non-standard parts used at net prices. Parts

which are standard dealer items can be purchasedfrom most electronic supply stores.

If transformers are returned for factory repairor exchange, they should be removed from theequipment without cutting the leads short. If leadshave been cut rather than unsoldered, so that theyare no longer usable, the guarantee on the trans­former is voided.

In the event that the assembled kit does notfunction properly or breaks down after some use,Dyna Company will service the kit for a servicefee of $7.50 plus the cost of parts which have beendamaged by the user or are past the guaranteeperiod. This service facility is not available forkits which are incompletely wired, or have beenwired with other than rosin core solder, or inwhich changes or modifications have been madewithout fa c tor y authorization. In addition, NOPARTS WILL BE REPLACED NOR WILL ANYSERVICE BE AVAILABLE FOR KITS WHERETHE GUARANTEE POST CARD HAS NOT BEENRETURNED. THE SERIAL NUMBER ON THISINSTRUCTION BOOK MUST BE MENTIONED IN

CORRESPONDENCE, PARTS RETURN, OR KITSRETURNED FOR FACTORY SERVICE. It is thefactory prerogative to limit the service facility toone year from date of purchase.

When shipping the amplifier for service, a notemust be attached specifying the symptoms, thename and address of the sender, and the serialnumber of the unit. The kit should be securelypacked with stuffing inside the cover to prevent thetubes from falling out of the sockets. It should beplaced in a rugged carton surrounded by severalinches of shredded paper or other soft packingmaterial. The original carton is not suitable forshipp ing a wired amplifier.

Shipment should be made by prepaid RailwayExpress, where possible; and repaired kits will bereturned by Railway Express COD for freight andservice charges unless these charges have beenprepaid. Parcel post is not a safe method forshipment of completed kits and should not be used.

Dyna Company assumes no responsibility orliability for dam age s or injuries sustained inassembly or operation of the Dynakit.

STEREO 70 PARTS LIST

(Parts of similar type which do not change performance may sometimes be included as a matter of expediency).

1 - Chassis set (including cover and bottom plate)1 - Power Transformer - PA-0602 - Output Transformers - A-4701 - Choke - C-3544 - Output Tubes - EL-341 - Rectifier Tube - GZ -342 - Driver Tubes - 71997 - Octal sockets1 - Printed Circuit Assembly - PC-31 - Filter Capacitor - Quad @ 525V2 - Capacitors - 50 MFD1 - Dual Ceramic Capacitor - 2 x .02 MFD1 - Selenium Rectifier2 - Four Screw Terminal Strips1 - Fuse Post plus rubber washer and mounting nut1 - Fuse - 3A Sio-Blo1 - Line Cord1 - On-Off Switch (SPST)1 - Input Switch (SPDT)1 - Dual Input Socket1 - Input Socket Insulator2 - Potentiometers 10,000 ohm1 - Seven Lug Terminal Strip ~

1 - Hank Wire

RESISTORS2 - 15.6 ohms4 - 1000 ohms (brown-black-red)2 - 10,000 ohms (brown-black-orange)2 - 470,000 ohms (yellow-violet-yellow)2 - 10 ohms (brown-black-black)1 - 6800 ohms (blue-grey-red)1 - 22,000 ohms (red-red-orange)

4 - Rubber Feet33 - 4/40 x 1/4" Screws31 - 4/40 Nuts30 - #4 Lockwashers

1 - 4/40 x 3/4" Screw4 - #6 Sheet Metal Screws

10 - 8/32 Screws14 - 8/32 Nuts14 - #8 Lockwashers

1 - Rubber Grommet2 - Solder Lugs2 - 3/8 Lockwashers2 - 3/8 Nuts2 - Cable Clamps1 - Set Instructions & Pictorials

11

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* MATCHED 1%o PREAMP POWER TAKEOFF POINTS

*Measurements at these points vary from tube to tube and donot indicate wbether performance is normal.

HMeasurements at these points can only be made with a vacuumtube voltmeter. The two tubes in a pair should have identicalreadings.

2ol10·yolt120·..,olt

1 -<VIOLET ~II WHITE

BLACKII WHITE

VIOLET ~

SPECIAL INSTRUCTIONS FOR OPTIONAL120.240 VOLT POWER TRANSFORMERS

BLACK

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 Operation1 ( ) 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 Operation1 ( ) 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 withelectrical tape.

When connected for 240 volt operation, a 1~ ampere slow blow fuseshould be used.

Printed circuit

Eyelets #3 and #18370 volts dc

Selenium rectifier

Bottom (+) lug 50 acTop (-) lug -65 dc

VOLTAGE TEST POINTS

Pin # Any EL-34 GZ-34 Either 7199

1 1.56 *2 -> 435 *3 410 *

u360 ac

u4 I'<l 415 oj 1->5 '<!' -32** ~-><.0 <D

6 -32** 360 ac 1.07 -> 08 1.56 435 *9 *

Capacitor lug

A • 305

B '" 375C 415D ... 435

117 V AC

PA-060

BL

+20

10K-+.50+.50

B~i C-.;,

22 K 6.8 K

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