Kenwood KA 907 Service Manual

Page 2

10

CIRCUIT DESCRIPTION

MC HEAD AMPLIFIER

5.
F
E
x I
L'
61 5
100171
+
g§ G1
:9 e« 99
x F
E 05 01 9" 015
*' cazooo x
3 8
mean»: x m
8 E ,.
' h - 3
w 0
=3 3 , *5
.- m
: Er GIBI
i I I

Fig. 1 MC Hlld Amplifier

The MC head amphher consusls of a Imeerslage, svmmemca
complememary clrceu. usmg low»no4se lrsnsismrs in the IHSI
slag:

An emmer IoHower circuit IS used m the final sIage so mat
the common emmer mmm m vhe second stage was
sulhcuem amulmer

Negatlve Ieeubauk hum me nnal slage emiuar .5 applied In
Khe Ivrsl sxage emnter, and the addmonal DC negaIlVE
feedback irom [he second SlagE emmer IS apphedm the IIISI
stage base which makes onevanon very 51am

The advamagos of mo complememary nlrcmt are'

1 AHhough Iransxswrs'OW and 03 05 and O7, and 09
and (111 are dlleCIW connecxea m serves, mesa causal
vansxsmrs can conduct as a DaraHed cxrcun Ior (he
outpu: and Input svgnals Consequently (he oulpm
Impedance can be lowered and a mgher ouxpu: voIlage
can be ubvamed

Z Push-pull opevauon reduces We dlswman

3 The cerUlI convuguuauon makes me best use of ma hxgh
S/N characlellsucs oI me vansusmrs.

POWER SAFETY INDICATOR cmcun
-_"_°£22°_'2E _______

To 02-: Lulluum

2 Powcr "fay indie-tor circuit

The LED meke-s Iuv ubuul ten seconds aner power-on and
becomes COHSIH'II by the molecnon reiav being energized
when all mean; In me KAVQO7 are mamlned an mam;
mumvmramr IS used to maker me LED

VGC

l

Fig. 3 Mable Multivibrahor

The Lambs muluwbramr comm: of two same Iran-aimed.
021 am: 022 Smelly. charactensncs u! transmora are
dufferem

When me CIICUIL I5 energized, GZI and 022. both DI the co"
lecvor curvsms flow

The conccmr currem DI euher cI two l5 \argerthen the mhar
because 04 hFE dsflerencs or the We

Assume. me coIlacwr quflem of Oil 5 large! than that CI
022

Page 3

CIRCUIT DESCRIPTION

« Cull-ct" mnnmulD! tlnm

Basil curt-III nf 921 um
J
Cull-nor mum cl an rum-u: . toll-cm vamp M Cm drop!

l t
am curront or mt Inmum. Base volt-gs nmzz amps

l l
Cull-cw valtsou 911122 Incl-uses. .7 Cnlhctnr caught at all damages

Fig. 4 (Duration of Amt-Mo Multivibrnor

ten the voltage al lAl lb Iuwer than at Hz) lBoth voltages
result lrom voltage drop across each collector load l
These voltages are apolled to IE) and (Cl through car and
C62. respectlvelv Slhce the base valtage at 021 l5 htgher
lhan Irml u! 022 mu collector current ul ozr llln'ter
Increases and that Cl 022 lurthar dacrsasas then stops
llnwmg

Then. DZl IS ON and 022 l5 0H- At thls tlme, the voltage at
each potnl ls as follaws (Al = O W 18) = 0 IV. ICI =
o N (Dl ~ +Vcc And {262 is charged atabcuthc

Than cat ts rrmrgtad through REE. so volrsgs s~ (El
gradually Increases When the voltage at law reaches about
0.6V. the cullecmr current al 022 stalls Howl-n9. reuumng
the voltage at lE) by the voltage drop across R84. Voltage
drug at lEl causes the voltaga at tcl. re the base voltage or
021. to drop Ihmugh C52

Than 02l ls cut a" C62 dtscharges through a path 0| lEl _.
R84 - HES a (Cl. but lt takes a canam ttme to comaletc
discharge because of hlgh resustanca ol R86 + RSI:
Tnsreture, cuz keeps the vct; voltage tor a tew seconds alter
021 l5 cut all

I;

Grand 101 Ind up»,
+ Vac tn (El

Una" (CI and (El

SlllCS 022 turns on, the voltage at (E) is lowered to about 2V
by the voltage drop across R84. Since the potential
dlflemma netween (Cl and lFl Is VCC, the voltage ath] 15(2
- vccl -VEC lRalertu Flg 5)

At thus lllllB. lllu vullagu dl Bdull pulnt is as follows. A =
+Vcc. (El 0 7V. IC) = +Vc(;(Dl = 0 lVendlEl = 2V
The voltage at [El ls about 2V hlgher than at ml by the
lurward voltage drop of LED and D12 Current enetglling
llle LED lnu>llv lluvvs lllluugh H57

Then. C62 ls gradually charged and vollaga at (cl lncreases
fmm -Vnr When the voltage at [Cl reaches 0 EN, 012 Is
lurrtad on and 022 I5 CHI 0". resulting m LtD all. At thls
(llllE, the valleys at each paint lsasfollnws (A) = o 1v. lBI
- +VCC.(Cl = 0 7V.(Dl - +VccandlE) = +Vcc.

The amt/p. nmnedttms are repeated and the LED flickers
Waverorm at each palm l5 shown th the lotlowmg chart

or.

(9
o
|

® a-
.t
3%
© - tr. P
PDWII " "
on

Fig. 8. WI Itnrm ll E-ch Palm

Alter lhs clrcuit operutlon become: stable. the protect-on
relay Is energtzed The collector voltage at the relay drive
transistor (224 l5 led to the bass Ell 023 through H73.
musmg 023 m uunduut 023 stuns lunctlon 0f the
muluvmratm by means cl D13 and D14. caus-ng the LED
keeping on llghlrng

w '°® ©
@vcc':> ::+: Ecfiywfij E ::> g J: we
(9 ©

Ground IE) Mums voluga at 1:) mm

(El mound-d

Fla. 5 Operation cl CS1 and (:62