Page 5 of 22
C72 are temperature compensating capacitors which insure stability
even in the 28 MHz band. Using the same dial mechanism as the FR-
lOOB, with the 50 kHz variation per revolution of the knob, it is
very effective for SSB and CW tuning.
Buffer amplifier Tr2, silicon transistor type 2SC372, is employed
in an emitter follower circuit. Its output is injected to the
first grid of mixer tube V2 (12AT7), and is also used as a VFO
source for the transmitter when connected for transceiving. The
output terminal is located on the rear panel of the receiver.
{
This output terminal is where I have connected a frequency
counter that displays the received frequency.
}
4. 1st I.F.
The signal converted into the 1st I.F., 5 173.9 kHz, by the 1st
mixer, is applied to the 2nd mixer via transformer L6.
5. 2nd Mixer
1st I.F. and 2
nd
local oscillator signals are added at the control
grid of V3, a 6CB6, and results in a second I.F. at 455 kHz at the
plate of the tube.
6. 2nd Local Oscillator
Tr3, silicon transistor type 2SC372, together with a quartz
crystal (X1) and other parts are installed in an I.F.T. case.
Output of the 2nd local oscillator is applied to the control grid
of V3 (6CB6) through transformer Ll9. Oscillator frequency is 5
628.9 kHz.
7. 2nd I.F. Amplifier
This is a two stage amplifier using two 6BA6 coupled by two 4 kHz
mechanical filters. "S" meter is inserted in the cathode circuit
of the second 6BA6 (V5) and must be adjusted to indicate zero with
no input signal. The "S" meter indicates cathode voltage
variation in V5, which is proportional to the AGC voltage. A
diode in series with the "S" meter protects it from inverse
deflection. Cathode return of V4 together with that of the RF
tube (V1) is connected to the RF GAIN potentiometer (VR1). {My
receiver as well as the schematics I have seen do not have this
diode in series with the “S” meter}
8. AM Detector & Noise Limiter Circuit
Gold bonded diode, 1Sl007 (D4), is used for AM detection. Series
type automatic noise limiter (ANL), with silicon diode 1Sl941 (D2)
effectively suppresses pulse noise. The ANL may be switched off at
the front panel.
9. SSB & CW Detector
Содержание FR-50B
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