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INITIAL ADJUSTMENT

Plug in the EL-34's (see pictorial) and the 7199

tube. Do not plug in the GZ-34/5AR4 rectifier yet. If

an ohmmeter is available measure the resistance from

capacitor lug #2 to ground (chassis). This should be

in excess of one hundred thousand ohms. Inspect wir-

ing to make sure that all joints are soldered and that

no parts are shorting together. Plug line cord into 117

volt AC outlet and turn on switch. While tubes are

warming up, set the bias potentiometer to the ap-

proximate center of its rotation. This setting is only

approximate and the amplifier should not be run

without following the directions below.

Your Dynakit includes Dyna Biaset (patent pend-'

ing) which greatly simplifies setting of the bias volt-

age. This can be done with the most simple and inex-

pensive types of DC meters as long as they have a

If in the course of bias setting it is found that the

control range of the potentiometer is insufficient to

obtain the correct setting, do not operate the ampli-

fier until the cause of the difficul ty is determined.

Operation with incorrect bias can lead to damage of

the output tubes

andlor

other components.

Note that the use of pin #8 as directed in the wir-

ing instructions means that this pin may not be used

as a connection for power takeoff for preamplifiers.

Most preamplifiers do not require the use of this pin;

however if use of pin #8 is indicated for your particu-

lar preamplifier, another unused pin must be chosen

for a bias voltage check point. If this is not possible,

the connection from the output tube pin #8 to the

power takeoff socket must be omitted; the bias volt-

age meter reading may then be made directly at the

#8 pin of either output tube.

PREAMPLIFIERS

The Dynakit Mark IV can be used with any con-

ventional preamplifier in monophonic or stereo sys-

tems. Preamplifiers which are self powered are con-

nected by simply plugging the signal or audio cable

into the input socket of the Mark IV. Preamplifiers

which are dependent on a power amplifier for their

power source are readily connected to the preamp

power takeoff octal socket on the Mark IV. The Mark

IV wiring instructions include the correct power take-

off connections for both the DYNAKIT PAM-l pre-

....

rating of ] 000 ohms per volt or higher. The correct

setting of the bias provides a total cathode current of

115 MA for the pair of EL-34's. This current through

the precision 13.5 ohm resistor produces a voltage

drop of exactly 1.56 volts DC, and this voltage can be

checked at pin #8 of the preamplifier power takeoff

socket. 1.56 volts is the voltage reading of a new type

D flashlight cell. Thus any fresh type D cell may be

used for an accurate reference for the bias voltage

setting.

The procedure for "etting the bias voltage is to

measure the voltage of a fresh type D cell and note

the meter indication. Then insert the positive meter

probe in the pin #8 hole of the preamp takeoff socket.

(Note that outside the chassis the pin numbers are

counted counter-clockwise from the key.) The nega-

tive meter probe should be applied to the chassis.

Plug in the GZ-34

15AR4

rectifier tube, and in about

ten seconds there will be a current flow which will

cause an indication on your meter. The bias poten-

tio'..rieter should be adjusted until the meter indicates

the same voltage as did the type D cell. There may be

a slight drifting of the voltage indication as the new

amplifier warms up for approximately the first 15

minutes, after which the bias control may be read-

justed. Thel'€after slight variations may be caused by

small changes in the supplied line voltage. These

variations will neither affect the

performanc(~

of the

unit, nor will it be necessary to readjust the bias set-

ting. The bias setting is a semi-permanent one and

need only be reset upon replacement of the output

tubes or at such time as other repairs or maintenance

might be required. A recheck at the time of mainten-

ance, or after a year or more of heavy usage, will hP.lp

preserve peak performance and keep distortion to an

absolute minimum.

Connect one end of a 7" wire to lug #4 of

the four screw terminal strip (8). Con-

nect the other end to eyelet #3 (8 l.

Connect one end of a 1000 ohm (brown-

black-red) resistor to eyelet #9 (8). Con-

nect the other end to pin #5 of socket V3

(8) .

Connect one end of a 3

wire to lug #2

of the bias potentiometer (8). Connect

the other end to eyelet #11 (S).

Connect one end of a 1000 ohm (brown-

black-red) resistor to lug #5 of V2 (8).

Connect the other end to eyelet # 10 (8).

Connect one end of a 3

1 /

2 "

wire to pin #4

of V3 (8). Connect the other end to eye-

let #7 (8

Connect one end of a 6800 ohm (blue-

gray-red) resistor to lug #2 of the quad

filter capacitor (8). Connect the other

end to lug #4 of the filter capacitor.

Connect one end of a 10" wire to lug #4

of the filter capacitor (8). Connect the

other end to eyelet #8 (8).

Connect one end of an 11" wire to'lug #3

of the filter capaci tor (8

Connect the

other end to eyelet #6 (8).

Separate the two conductors of the line

cord for about 2

1 /

2 ".

Cut about 1" from

one of the conductors, then strip and tin

both. Insert the line cord through the

grommet from the outside and push

enough through to tie a knot about 4"

from the end. Pull the cord back until

the knot is snug against the grommet.

Connect the short lead to lug A of the

fuse post (8). Connect the other lead to

lug #1 of the slide switch (8).

It is wise to go back and check all connections for

correctness and for good soldering. All hardware

should also be checked for tightness. The fuse can

now be installed in the fuse post. The rubber feet

should be installed in the proper holes in the bottom

of the bottom plate.