Akai VS-2EGN

9-4 AUDIO MODULATOR CIRCUIT
tl
| RE clo
P TO VIDEO
* MODULATOR
Fig. 7-123 Clapp OSC
1) In Fig. 7-122, TR1 is AUDIO AMP, and 50 us pre-
emphasis is provided by RS and C2.
2) TR2 is an oscillator transistor, Fig. 7-123 shows the
equivalent circuit. This is a Clapp OSC. T1 of Fig. 7-
122 corresponds to L of Fig. 7-123, and the sub-carrier
frequency is adjusted by this component.
3) A sufficiently large audio signal is applied to the base
of TR2 (base bias voltage). The base input capacity chan-
ges in proportion to the change in this voltage. Asa re-
sult, the oscillation frequency of this circuit changes.
Audio frequency modulation is performed based there-
on. The center oscillation frequency is 5.5 MHz (in the
case of EG and EGN models). Frequency is adjusted by
T1 of Fig. 7-122.
4) The sub-carrier signal subjected to frequency modu-
lation enters the video modulator, modulates the carrier
together with the video signal, and becomes the RF out-
put. Fig. 7-124 shows its frequency spectumm.
Service Manual VS-2EGN
Fig. 7-122 Audio Modulator
fp
fp=VIDEO CARRIER
fco=COLOR CARRIER
fs=AUDIO CARRIER
fe
‘S.SMHz-
(for EGN model)
Fig. 7-124 RF output frequency spectrum
83