Hitachi TRQ 700 Service Manual

Page 1

In this service manual, (E) and (U) are expressing those
sets exported mainly for Europe and United States respec-
tively. Also, as a trial, some circuitry explanations are
given. For better after servicingI only go through directly
to page 6.

( - ) Hitachi Sales Corp.

48-50, 34th Street, Long Island City, NY. 11101

HITACHI TAPE RECORDER
MODEL ERG-700

SERVICE MANUAL

No. 125 1966

SPECIFICATIONS

ELECTRICAL CHARACTERISTICS
Power Consumption. ......55 Watts. (Maximum)
Biasing System. . ..AC Bias.

Erasing System. . AC Erasing.
Mains Frequency. ..50/60 7:.
Overall S/N ................... More than 40 dB.

Bias Oscillation

FIEquency.
Bias Current. ..
Erasing Curren
Input Impedance.

.Microphone Jack ...... 6 kD.(U), (E)
Radio In Jack ...... 330 kfl(U)
REC/P. B. SOCKET ...... Line-in 50 k0} (E)

Line-out 6000
...Ext SP. ......8.Q.

Output Impedance...

Maximum
Performance Time....90 minuttes at 7% (7'35micron)

3 hours at 3% (7"35micron)

6 hours at 1% (735micron)
...Within 4 minuttes. (7 reel)
Within 4 minuttes. (7" reel)
Push Button.

...Capstnn Drive.

Rewinding Time.
Fast Forwarding Tim
Operating System.
Driving System.
COMPONENTS USED.
Transistors. .................. 25373. 25375 X 3,
25B89 and 25B370 x 4.

Silicon Rectifiers. .

Microphone. .................. Dynamic Microphone. (2000.)

Motor. ...2poles. shaded pole induction motor. MISCELLANEOUS SPECIFICATIONS.
(Secondary winding provided.) System. .................. Monaural Dual Track.
Sound Output .3 Watts Dimensions. ........ Width : 136
Speaker ......... .6x4 80/400 91. Height I 7115'
MECHANICAL CHARACTERISTICS. Depth : 121,6'
Tape Speed. Weight. ........................ 16.5 lbs.
(Three speeds) ......... 7% per second 312%
3% par second 12%
1% per second i295
ACCESSORIES
Dynamic Microphone. (NDM-15) (U). (E) 1 Magnetic Earphone. (U) l
5 Magnetic Recording Tape. (U) 1 Power Cord. (E)
5 Empty Reel. (U),(E) 1 Extension cord (U) I
Splicing Tape. (U) 1
FEATURES

Hitachi's unique levelmatic device adopted.

Push-button system easy to operate.

Quick movement due to all transistor system.

Rich sound with large output of SW.

Front speaker system using large sized 6x4 speaker.
Three speed (7%. 3%. 1%/sec.) system.

99??!9!

7. Tone control provided.

8. Long time recording of 6 hours is possible using 7 (3511)
tape.

9. The cover is shut down with the 5" tape, reel and the
accessories are kept inside the cabinet

Page 2

MODEL TKO-700 SERVICE MANUAL

CIRCUIT EXPLANATION

GENERAL DESCRIPTION

Because this model is a 3 speed High Fidelity Tape-recorder
for home use, we made pretty many efforts on improvements
of Frequency Characteristics and Distortion.

Gain and frequency characteristics are varied in one ampli-
fier by means of switching R-C circuit on and off to obtain
desirable characteristics corresponding to recording amplifier
and playback amplifier.

Generally, comparison of output voltage from magnetic
recording head and microphone shows that the latter exceeds
about 10 dB. This means that the gain of recording amplifier
may be less than that of playback amplifier by 20 dB.
Following are explanations on Negative Feedback and Tone
Control circuit in the first stage, RC circuit employed between
2nd and 3rd stage, newly developed levelmatic circuit and
finally Bias Oscillator circuit.

THE FIRST STAGE.
There is no difference from other Hitachi Tape-recorders,
as far as the input circuit of the first stage is concerned.
R2 and C1 is to eliminate radio broadcast signal at places
near a transmitting station and R4 is a series resistor to
raise input impedance and to regulate bease signal current of
first stage so that it would not be varied much in accordance
with signal frequency.
At the time of playback, C7 and VR2 are constituting series
tone-control circuit in collector circuit through DC blocking
capacitor C4. 32 in parallel with the tonecontrol circuit is
to eliminate hissing sound, generated mainly at first stage
at stop condition, and is switched on and off together with
function selector keys. (Fig. 1-A)
At the time of recording, a negative feedback is given to
base of first stage from collector of the same stage.
The frequency characteristics of this NF is flat i. e. regardless
of frequencies. (Fig. 1-B)
In emitter circuit, R9 (820 D.) and C33 parallel circuit -is
connected but, as value of C33 is so small (0.022 mF),
considerably bigger voltage in low and middle frequency are
fed back negatively to boost up the high frequency com-
ponents. (Fig 2, 3)

(NEGATlVE FEEDBACK) TYPE
-F BOOSTER,

Fig. 2

TRI
c5
C4
mo
Slr4
c7 2

s
LEVER SWITCH
VRZ
(TONE)
1-A

Fig .

L
[I

=04

Sl~4
Fig. 1-3

At the time of recording, instead of NF type high frequency
booster, levelmatic circuit is brought into emitter circuit
This will be explained later.

RELATIVE CONSIDERAELY LARGE VOLTAGES ARE NEGATXVELY FED
RESPONSE. BACK IN LOW AND MIDDLE FREQUENCY RANGE.

RESPONSE WlTHOUT C 33

W

IOOOO FREQUENCY 9g

Fig. 3 HIGH FREQUENCY BOOSTING.