Dynaco Dynakit Preamp Owners Manual

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INSTRUCTIONS FOR ASSEMBLING THE DYNAKIT PREAMPLIFIER

Price $1.00

'U 5 PAY, PEND.

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INSTRUCTIORS FOR ASSEMBLING THE DYNAKIT PREAMPLIFIER

DESCRIPTION

Your Dynakit preamplifier is a versatile preampli-
fier control unit which permits using any modern pro-
gram source with your Dynakit or other power ampli-
fier. This preamplifier uses a new circuit (patent pend-
ing) in which both voltage and current feedback loops
include every tube section. These feedback loops give
tremendous stability and consistency of performance.
greatly reduced distortion, and exceptionally low noise.

The Dynakit preamplifier contains an unusual design
arrangement. A single 12AX7 tube acting as a feedback
pair with ewalization determined by feedback at fre-
quency extremes acts as a low level amplifier for
magnetic cartridges. microphone. or tape head. This
section has a voltage gain of 50 to bring up low level
sources to a point comparable to inputs from high level
sources such as radio tuners. tape recorders. etc. A
second l2AX7. acting as a similar feedback pair. is the
tone control section; and tone control action is adjusted
by control of feedback at frequency extremes. This
section has a voltage gain of 10 bringing the various
inputs up to a high enough level to energize any popular
power amplifier.

A volume control and switching system interconnects
these two feedback pairs. By this type of arrangement,
signals are attenuated before going into the tone control
section so that there is no possibility of overloading
regardless of the amplitude of the signal source. There-
fore, distortion is unaffected by the position of the
volume control. in many preamplifiers distortion islow-
est with the volume wide open but rises significantly
with the volume in the normal listening positions. This
is not true with the Dynakit preamplifier.

The circuit arrangement used also eliminates fre-
quency discrimination for different positions of the vol-
ume control. In much equipment on the market the high
frequency response is lost when volume is reduced. This
is not true in the Dynakit preamplifier where nothing is
changed except the total gain by varying the volume
control.

The Dynakit preamplifier is intended as a complete
control unit so that there is no need to have the power
amplifier in a convenient location. All switching of the
audio circuits as well as control of the ac power to the
auxiliary equipment is controlled from the preamplifier.
A built in rectifier supply which converts the filament
current to do permits extremely quiet operation regard-
less of the power source to which the preamplifier is
connected. These features make the Dynakit preamplifier
completely independent of the type of circuitry from which
it is powered.

GENERA L WIRING PRA CTIC E

Assembly of the Dynakit preamplifier is quite simple
compared to general kit assembly requirements. This is
true because all critical parts of the Dynaklt are factory
assembled for you on the printed circuit assembly. Other
parts are put out in the open through a free and un-
cluttered layout so there is easy accessibility for wiring
or trouble shooting purposes. Construction ofyour Dyna-
kit should not take more than about six hours because
of these simplifications.

Tools required for easy assembly of your Dynakitare
soldering iron (small tip) or soldering gun. long nose
pliers. screwdriver, and wire cutters. Although not es-
sential. 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
satisfactory results from any electronic equipment. ALL
SOLDERING MUST BE DONE WITH ROSlN CORE SOL-
DER. 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." Wheneversoldcr-
ing is required. the assembly instructions specify it by
(5). if this symbol is not shown after 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 shouldbe held in place for
a few seconds and removedwhen it is seen that the solder
has contacted both parts of the connection - the lug and
the wire to which itis connected. It should not show a ball
of solder but a smooth transition from solder to compon-
ent lead.

Before applying solder the joint should be clean and
the lead should be crimped in place so as to have mech-
anical 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 ifthe lead is wiggled with a
pair of pliers. 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
soldering gun is used, it should be used with discretion
since the amount of heat available is far more than
required for soldering light wires.

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IN CASE OF TROUBLE

Although your Dynakit preamplifier has been made as
trouble free as possible. there is always the possibility
that a mistake inassemblyoradefective part will prevent
it from functioning properly. Therefore ifany difficulties
are encountered. the following routine should be estab-
lished.

Check the wiring carefully. making sure that all con-
nections are made and soldered. that adjacent parts are
not touching. and thatno pieces of solder or wire clippings
have gone . -ross adjacent points. causing shorts.

Make sure that tube filaments are lit. These do not
light brightly but should be visible under dim light con-
ditions. If tubes are unlit this indicates (ilhtf a break in
the power cable. a fault in the rectifier. or an open
filament in the tubes. However if the pilot light works,
this indicates that the power cable is functioning and this
can be eliminated (at least for the heater winding) as a
source of trouble.

Another test which can be inzldewithoul instruments is
to try feeding a signal into the radio input from a tuncr or
other source known to be in functioning condition. Switch
to radio input when making this test. Thcnihe two 12 X7
tubes should be interchanged and the test tried again. If
Signal comes through in one case and not with the tubes
interchanged. it indicates a defective tube. If signals come
through the radio input satisfactorily, but not through the
phone input. at least the trouble has been localized to the
phone section alone. A similar test to see whether or not
the phone section is functioning while the tone control cir-
cuits are inoperative is to feed a signal into the phono-
graph input (this can be a signal from any source. al-
though a high level source such . .t tuner will not sound
good because of improper equalization and overloading).
and lake output from the tape output socket which pre-
cedes the tone control section of the preamplifier. How-
ever. in making this test there is nocontrol of the volume
of the signal andit may possiblycausc overload signals to
go through the amplifier. This test should notbe made un-
less a finger is kept on the amplifier switch so it can be
turned off immediately if the sound level gets too high.

If the above tests permit isolating the fault to one or
the other section of the preamplifier. then that section of
course should be carefully checked. Any other type of ser-
vice work which can he done. should have the use of test
equipment of which the minimum item should be a high
grade voltmeter, preferable a vacuum tube voltmctcrora
20.000 ohms per volt meter.

Voltage measurements should be made and compared
with the enclosed voltage chart. Deviations ofgrcater than
10% from these voltages may be an indication of mal-
functioning. although deviations as high as 5071 will not
cause complete lack of sound.

In the event that the preamplifier is functioning, but
that sound is distorted. or the noise level is high. a

check should he made of the wiring and of the voltages.
Any serious discrepancy in voltage may indicate an open
or shorted resistor which can only be checked by mea-
surement of the component. Excessive noise must be se-
parated as to whether it is hum or hiss. lluni is a com-
pletely different type of problem than hiss. and proper
trouble shooting must separate one of these distruhunces
from the other.

Hum ls generallybccause cfpoor grounding in the pre-
amplifier or assoei: ed equipment or in a defect in the
heater voltage doubler circuit. lliss is almost invariably
due to a noisy rcsxstor.and the most common culprits arc
the plate and cathode resistors in the first stages. There
should be practically no hiss when thcprcamp is switched
on radio position. If thereis.thc 470.000 ohm plate resis-
tor or the 47m) ohm cathode resistor of the 12AX7 are
most likely to be at fault. The : should be substituted
with corresponding values of half watt resistor. If the
hiss comes from the phone section. (noise in the phone
section will be affected by settings of the volume control
while noise in the tone control section is independent of
volume settings: this identifies the portion of the circuit
in which the noise originates) it is most likely due to
either the 270.000 ohm plate resistor or 2200 ohm cathode
resistor of the 12AX7. These should be removed (without
damaging them) and replaced with similar resistors to
see whether it cures the trouble. If not. reinstate the
original resistors which are of a type which should pro-
duce very low noise.

Please note that when the cover is not on the pre-
amplifier. thc hum level will be many times higher than
when the cover is on and properly closed with the sheet
metal screws. Therefore. testing should be done only
with the cover secured in place.

FACTORY SERVICE AND GUARANIY

All parts in the Dynakit are guaranteed ior a period
of one year. except for tubes which carry the standard
l-Zl.-\ guarantee of 00 days. and defective components will
bc replaced without charge if returned to the factory
directly or via your dealer. Many dealers carry Dynakit
spare parts in stock to facilitate replacements. After the
guarantee period. parts are charged for at regular net
prices.

in the event that the assembled kit does not function
properly or breaks down after some use. Dyna Company
will service the kit for : service fee of $5.00 plus the
cost of parts which have been damagedby 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 have been made without factory authorization. In
addition. St) PARTS WILL BE Rillljtclil) NOR WILL
ANY SERVICE BE AVAILABLE FOR KITS WHERE THE
GUARAN'IEE POST CARD HAS NOT BEEN RETURNED.
TIIE SERIAL NUMBER ON THIS INSTRUCTION BOOK
MUST BE MENTIONED IN CORRESPONDENCE. PARTS

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