Adjustment Of Amplifier; Adjustment Of Recording Bias Frequency; Adjustment Of Recording Bias Voltage; Adjustment Of Erasing Bias Voltage - Akai 1700 Service Manual

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ADJUSTMENT OF AMPLIFIER
r. ADJUSTMENT OF RECORDING BIAS FREQUENCY
Rccording/crasing bias frcquctrcy was set at 90 KC plus or m;nus 5 KC before sh;pment. It is decided by inductance
otthc oscillato. coit lpart * l7-L,) and its resonant capac;tor (part f C-17). To mcasu.e recordiDg bias frcquency, insert
a l0 or 100 ohm resisto. ;n scrics to the .cco.d/play head and coDnect vertical ;dput te.minals of an oscillos.ope as showq
in the Fig. 13. ADothcr testirg instrument to be prepared is an audio frcquency oscillator and jtsoutput shouid be conDe-
cted to hor;zontal input terminals .,f the oscilloscope. Vary frequcncy gene.ated by tbe audio frequency oscillator around
90 KC, and set the oscillator at the point whe.r a desirous 6gurc appears on the oscilloscopc.
'fhc
recordins bias frequcncy
no$' corrcsponds to the reading of the oscillator. Check oscillator coil, C-17 and bias head if the recording bias frcqucncy
mcasu.ed ; not w;thin 90 KC + 5 KC.
2, ADJUSTMENT OF RDCORDING BIAS VOLTAGE
A p.oper rccordnrg bias vottagc is 45 volts + 3 volts A.C.
and is adjusted by Cl6. To measure .eco.ding bias voltage,
coDD€ct a V.T.V.M. (Vacuum Tube Volt Mete.) to the record
/play head as showD ;r the lig. 14.
Check Cl6
(included AKl3)
and record/play head if the
recording bias voltage mcasu.ed does not meet to th€ abovc-
mentioned specificatioD.
L 1 { 0 , s . c )
Fig. 13
l i '
- I
j ( P l l L E F T ]
Hi|mn-!,(c,lEIcHr)
I#ltlri!i
F;g. 14
3. ADJUSTMENT OF ERASING BIAS VOLTACE
A prope. €rasing bias voltagc is 65 volts + 5 volts A.C. and is adjusted by Cl4. To neasure erasing bias voltage, connect
a V.'[.V.M. to the erase head as rhown in the Fig. 15.
Chcck Cl4 and crasc head il thc oasing bias voltage measured does not meet to the above,mentioned spe€ification.
Fig. 15
4. ADJUSTMENT OF RECORDING LEVEL
A basic rccording lcvcl, .cfefcd to as "oVU", s€t at th€ point where
current of 30lA + l0 % flows to the recording head at 1,000 cycl€s.
The VU neter indicates oVU ! 2 VU wheD a signal of -55 db + 5 db
at the microphone jack or -40db
+ 5db at the line input jack when
thc volumc control set at its maximum.
Adjustment ot recording level can be accomplishcd by varying sensi-
tivity of VU metft, however, it is not necesa.y to make in a field of
service as all VU mete6 have co..ectly been calibrated at factory befor€
shipment. (See lig. l6 for details.)
NOTEi Make sure to stop oscillation by disconnecting the oscillator
coil | 17-L, at the points marked "P" and "G" prior to measure,
ment of reco.ding lcvct.
i f^-
o;.---r:@*=;;'6d.".0,.-""
#;;;-v'1c'
lRrcHr)
I;':I:::j-:-
v ' 1i,l l1 LE FT )
v , ( P ) ( R r c H T )
o-, ^ -,nrl
ll,,n r r"
Fig. t6