background image

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

Страница 1: ...Page 1 of 22 INSTRUCTION MANUAL FR 50B ...

Страница 2: ...ed sized and weights to metric Any errors I found have been corrected I have resisted making wholesale changes to the language used in the original instruction where I have added comments these are in italics References to AVC have been changed to AGC Version 17 December 2018 ...

Страница 3: ...ng on the same frequency is possible This is a useful feature for SSB communication A built in monitor circuit enables monitoring of the station transmitted signal at any time SPECIFICATIONS Frequency range 80m 3 5 3 8 MHz 40m 7 0 7 5 MHz 20m 14 0 14 5 MHz 15m 21 0 21 5 MHz 10m 28 0 29 2 MHz JJY WWV 10 0 10 5 MHz can be installed The AUX position on my receiver covered 1 2 1 7 MHz and appeared to ...

Страница 4: ...ange A FM type variable condenser is used with electronic band spread for pre selector tuning The centre of each amateur band is approximately at the centre of the range of the pre selector control On the 3 5 MHz band the pre selector covers 3 5 3 8 MHz 2 1st Mixer The amplified signal and local oscillator output are mixed by introducing to the grid and cathode of triode mixer V2 12AT7 The triode ...

Страница 5: ... 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 in...

Страница 6: ...ol VRl and monitor control VR2 are in series to cathode return circuit of Vl and V4 For muting with a transmitter relay contacts must open on transmit and close on receive Thus on receive the mute terminal is grounded On transmit the monitor potentiometer increases the bias The relay mentioned here is part of the FL 50B transmitter 12 A F Amplifier Output from the detector through the mode switch ...

Страница 7: ... ANL Off CALIB Off Monitor Minimum position AGC Fast CH select VFO Main dial may be accurately set for each band at the 100 kHz points with the aid of a crystal calibrator and adjusting the zero set control to zero beat Turn the main tuning knob to receive the desired signal and adjust for maximum S meter reading then peak with pre selector When impulse noise such as generated by auto ignition sys...

Страница 8: ...s possible to connect to the VFO When using a transmitter other than the FL 5OB the mute terminal must be so connected as to be open circuited to ground during transmitting and short circuited during receiving If receiver is used while disconnected from the transmitter M G terminals must be shorted together 5 Transceive Operation Set the Xtal switch of the FL 50B in EXT OSC position Switch to SPOT...

Страница 9: ... voltages than those shown in the table 2bis Resistance Measurements To further assist with fault finding Table 2 contains expected resistance measurements between ground and the indicated point in the circuit These measurements are made with the receiver switched off and preferably with the plug pulled out of the mains socket 3 455 kHz I F Alignment Apply a 455 kHz signal to grid 1 of V3 pin 1 Ad...

Страница 10: ...SG output 3 5 MHz and preselector VC1 at 1 adjust TCl and TC6 for maximum S meter reading On this band the upper limit of the preselector range is about 3 8 MHz so a slight sensitivity decrease results between 3 8 and 4 MHz During the alignment keep the SSG output level down to the minimum of that required at least below 60 dBm TC4 and TC9 are used to adjust the AUX frequency I have no idea what T...

Страница 11: ...0 6 35 Table 1 Voltage measurements ѻ Calibrator switched on Mode switch in SSB CW position no idea and no indication on any of my reference documents RESISTANCE MEASUREMENTS ohms TUBE PIN NUMBER 1 2 3 4 5 6 7 8 9 V1 150 6K 18K 0 V2 100K ѻ 1M 0 100K 100K 270 0 V3 100K 330 52K 500K 0 V4 0 5K8 30K 180 V5 0 5K6 11K5 150 V6 22K 220 34K 20K 4K7 V7 47K 0 70K 70K 220 V8 500K 220 470K 3K6 9K5 2K2 300K Tab...

Страница 12: ...circuit in the H T or heater circuits or failure of one or more of the silicon diode rectifiers D5 D6 D7 D8 2 No sound from speaker Examine speaker connections making sure that the headphone plug is removed from the jack on the front panel Check audio amplifier section by touching grid of V8 with a screwdriver Check detector stages AM detector diode D4 SSB BFO and product detector 3 Audio and dete...

Страница 13: ...ns The knob skirt may be adjusted independently of the knob itself by firmly holding the knob while turning the skirt and can be set at 0 for 100 kHz points with a crystal calibrator Since on all bands except 10m the knob rotates two full turns for each 100 kHz segment a double numbering system is adopted on the skirt thus read 0 to 49 kHz using the black numbers and 50 to 100 kHz using the red nu...

Страница 14: ...Page 14 of 22 PART LOCATIONS ...

Страница 15: ...Page 15 of 22 ...

Страница 16: ...Page 16 of 22 CIRCUIT DIAGRAMS ...

Страница 17: ...Page 17 of 22 ...

Страница 18: ...Page 18 of 22 ...

Страница 19: ...Page 19 of 22 ...

Страница 20: ...Page 20 of 22 ...

Страница 21: ...Page 21 of 22 This page is set to print landscape A3 ...

Страница 22: ...Page 22 of 22 This page is set to print landscape on a piece of paper 54cm wide by 25cm high ...

Отзывы: