through the control winding lowers the frequency of
deviation at the higher audio frequencies for equal
oscillation.
Since the core material exhibits slight
amplitude of audio signal applied to V10. To obtain a
permanent magnetic characteristics, it is necessary to
uniform deviation over the higher modulating frequency
increase the bias current momentarily to a value
range, C49 is adjusted to decrease the signal amplitude to
considerably exceeding that flowing at the operating point
V10. The signal applied to V10 is decreased at a rate
to prevent a center frequency shift when modulation first
equal to that at which V10 and V11 tend to produce the
is applied. This is accomplished automatically by the
greater deviation.
Capacitor C49 reduces the grid
surge circuit (para. 51), which delivers a positive pulse to
impedance of V10, hence the proportion of modulating
the modulator and the control winding; this stabilizes the
signal applied, as the frequency of the modulation signal
reactor at its operating point.
increases. The adjustment of C49 usually is made only
b. For stability of operation V10 and V11 are
when L1 is replaced.
connected in a degenerative feed-back circuit. The audio
signal voltage from the deviation multiplier is applied
44. First Doubler V6
across grid resistor RT1 of V10 through the T-pad
attenuating network consisting of R82, R81, and R80.
C21 (fig. 9) to the grid of first doubler V6 (fig. 11). Grid
After amplification and inversion by V10, the audio signal
current flowing through grid return resistor R41 produces
developed across R67 is coupled by C51 to the grid of
the necessary self-bias.
V11. Resistor R73 serves as the grid resistor of V11.
Cathode resistor R74 is the source of bias and is
unbypassed to introduce a small amount of degeneration
at all frequencies. Tube V11 also amplifies and inverts
the audio signal. A portion of the audio output voltage
developed across R69 and R70 appears across resistors
R66 and R65 which serve as the cathode resistor of V10.
The positive de potential, obtained in addition to the
voltage drop produced by normal tube current flow at the
arm of R66, serves as the bias voltage for V10.
Potentiometer R65 DEV COMP sets the minimum
cathode resistance and establishes the minimum
operating bias. Potentiometer R66 controls the amount of
out-of-phase audio feed-back voltage which is introduced
between cathode and ground of V10. This potentiometer
is linked mechanically to the TUNING control of the signal
generator. As the TUNING control is turned from the
lowest to the highest frequency, the amount of
degenerative feed-back voltage applied to V10 is
increased and the audio current flowing in L1 is
decreased. This is done to provide a uniform frequency
deviation over the entire range of operating frequencies,
since equal changes of inductance in the signal winding of
Figure 11. First doubler stage.
L1 produce a greater deviation at higher frequencies than
b. The plate load of V6 is the tuned circuit
at lower frequencies. By decreasing the amount of signal
composed of L3, split-stator tuning capacitor C24, and
voltage that is applied to the control winding of L1, the
trimmer Capacitors C23 and C25. Capacitor C24A and
inductance of the signal winding is decreased
C24B is ganged to the TUNING control and tunes this
proportionately to maintain uniform frequency deviation.
stage to twice the fundamental oscillator frequency (47.5
to 100 mc). Resistor R45, connected across the tuned
circuit, broadens the frequency response of the circuit to
handle the wide frequency deviation. The 200-volt re-
gulated plate supply voltage for V6 is applied through
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