Heathkit SB-401 - Page 53

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TO RECEIVE
AUDIO
Br RED
OUTPUT
Paeviat
T3 QOLEVEL To
AUDIO SPEAKER
OUTPUT Ag6 coe
TRANS 506 TRANSMIT
FORMER =
TO vox BLU
AMPLIFIER v12C
BO, 3 6DIO
e SIDETONE
TO BIAS alee / AMP.
SUPPLY Q}---=-
x
~%)
+10/35 RI39
T 470
V13B
1/2 6JI1
TONE OSC. RIS4
PISS
1M
Cl44
Figure 6-4
TONE OSCILLATOR AND TONE AMPLIFIER
(Figure 6-4)
Tone oscillator V13B operates only when the
Mode switch is in the CW position, The output
audio frequency (approximately 1000 Hz) is
determined by the phase shift network (P.E.C.).
This audio tone is used to perform two func-
tions: first, to key the VOX amplifier so that
break-in CW operation is instantaneous with the
closing of the key; and second, the output of
tone amplifier V12C is coupled to the receiver
speaker (by relay RL1) sothe operator may hear
his keying during transmission,
Grid-block type key control is used for V13B,
The output level of V13B tothe receiver speaker
is adjusted by control R38 to suit the individual
requirements,