BFO and Amplifier, Product Detector and Audio Amplifiers


To learn about the BFO and Amplifier, read the
Circuit Details - BFO/Amplifier
before building this section.

To learn about the Product Detector, read the
Circuit Details - Product Detector
before building this section.

BFO, BFO Amplifier, Product Detector, and 455kHz Filter

Approximate time to complete 0:40 - Picture | Picture

Insert all the components that have their values inside the footprint. They are the following:

____7 - .01 capacitors (Bag 3)

Solder

____3 - 100 ohm resistors (brown, black, brown) (Bag 3) Be careful, rectangle footprints only, there is a 100pf capacitor in the area.

Solder

____3 - 100K resistors (brown, black, yellow) (Bag 3)

Solder

Resistors:

____1 - 12K (Bag 4), Located above the MOSFET on the right side.

Solder

Capacitors (Going left to right on the board):

____1 - 100pf NPO (Bag 3), Located to the left of the 2N5486. Orange color, short leads flared out, labeled "101".
____1 - 3.3pf NPO (Bag 4), Located to the right of the 2N5486. Orange colored, small square, leads flared out, labeled "3R3 D", or short leads, grey with black top, labeled "3R3" (R looks like a P).
____1 - 47pf NPO (Bag 5), Located to the left of the Minicircuits T1-1T transformer. Orange colored, small square, labeled "470, JCC"
____1 - 2.2mfd Electrolytic (Bag 4), Next to 7805 Regulator, please note that the negative (-) side of part is marked. The + (Plus) side is marked on the silkscreen.

Solder

Other Parts:

____1 - 50A03 455KHz IF can, Black core (Bag 6), Located below the text "455 kHz BFO". After inserting into the board, touch the soldering iron to the IF can pins first, and make sure the pin is accepting solder before flowing solder onto the PCB.
____1 - 50A01 455KHz IF can, Yellow core (Bag 6), Located next to the product detector. After inserting into the board, touch the soldering iron to the IF can pins first, and make sure the pin is accepting solder before flowing solder onto the PCB.
____1 - 2N5486 (Bag 4), Spread the end pins slightly so they fit through the holes. Do not force all the way down onto the PCB and stress the pins. Note flat side of part and match to the flat side of the footprint.
____1 - 7805 Voltage Regulator (Bag 5), notice the text "Front" on the silkscreen and place the front of the regulator (heat sink is back of regulator) as shown on the silkscreen. Labeled "L7805CV".
____1 - 100K trim pot (Bag 5), located above the MOSFET, black or blue color, turn adjustment screw all the way counterclockwise, this gives maximum gain for initial testing and use. Black color, marked "EXP 104" on side. Blue color are smaller than the 10K blue trimmers, marked "104Fd5" on side.
____1 - LED (Bag 3), Red color. Match the flat on the LED to the flat on the footprint. The short lead is on the same side as the flat. Note: If you ordered the Super Bright LEDs, one can be placed here. For details, check Modifying the LEDs.

Solder

____1 - MOSFET (Bag 2), (Picture) static sensitive part, touch a ground wire before taking it out of the bag, notice the dot on MOSFET (may be difficult to see, hold at an angle to a light source and you can see the shadow of the dot), the dot is located to the left of the second line of the text on the MOSFET.
A dot is placed outside the footprint so that you can double check your placement after it has been soldered to the PCB. The leads on each side of the part need to spread apart slightly to fit the footprint.
____4 - HP5082 diodes (Bag 4), Blue band, on a reel strip all together. Note the band on the part and match it to the band on the footprint.
Bend the leads about 1/8" away from the body of the diode for easy insertion into the PCB.
____1 - T1-1T Minicircuits 1:1 transformer (Bag 4), Note the dot on the part and match it to the dot on the footprint. A dot is outside the footprint so that you can double check your work after it is mounted.

Note: Tin all the leads on the transformer as the pads they solder to are small. This will make a solid solder joint. Wipe the excess solder to the top of the pin so it will fit in the holes.

____1 - L40 B2 455KHz Filter (Bag 6), White color, another part with fragile pins, do not bend the pins when mounting/soldering the part to the PCB. Tin the leads with solder to get a good solder joint on the PCB.
There are two footprints for 455KHz IF Filters, only one is used. Use the footprint that fits the pins of your part.

If this part has a pin not soldered correctly, the S-Meter will show a noise level and indicate signals as you tune through a band, but no output at the speaker.

Solder

BFO Capacitor

____35pf small panel mount capacitor (Bag 1), with the numbers "193-10" on top, solder a 1 1/2" bare wire going down on each solder lug.
____Mount the capacitor on the board with the wires running through the left hole of the "Ground" square (this hole is also offset downward from the others) and the "BFO Tune" hole at the end of the silkscreen line.

____Pull down on the wires as tightly as possible underneath the board and then solder.
____Check the capacitor for a firm mounting before clipping the wires. If loose, reheat the solder on the loose wire and retighten.

Mounting a Knob on the Shaft

Note: The shaft of the BFO capacitor is 3/16". It is very hard to find a knob for a 3/16" shaft. By using the heat shrink tubing supplied with the kit, a collar can be made that will let 1/4" knobs work on the capacitor.

____Get the piece of shrink tubing (Bag 6). Put the end over the shaft of the capacitor and heat carefully with a lighter.
____Cut the end off the shaft when finished. Put another piece over the one just shrunk, cut off end - should be a tight fit.

____Install a 1/4" knob. Tighten set screws securely.

Securing the BFO Capacitor

When the BFO cap is level, there is a 1/16" gap between the capacitor and the board. When tuning the BFO, movement when tuning will cause the BFO to change in tone making it difficult to set exactly as preferred.

Arrow shows where to put the small line of glue. Don't overdo it here as it can get into the stator plates.

The method used here is to fill in the gap with epoxy or instant glue. This secures the BFO cap and prevents movement when tuning. The instant gel is easier to use and stays in place. Use just a little on the left side of the BFO cap.

Audio Amplifiers

To learn about the Audio Circuit, read the
Circuit Details - Audio Amplifiers
before building this section.

Approximate time to complete 0:45 - Picture

Insert all the components that have their values inside the footprint. They are the following:

____2 - .01 capacitors (Bag 3)
____1 - 100K resistors (brown, black, yellow) (Bag 3)

Solder

Resistors:

____1 - 1K (Bag 3), Located above the 5.6K resistor.
____1 - 10K (Bag 4), Located below the 2N3904.
____1 - 100 ohm (Bag 3), Located below the 2.2mfd Electrolytic and above left of the 2N3904 in the 'Audio Pre-Amp'. The footprint says 470, but the value has been changed to a 100 ohm resistor to improve gain.
____1 - 560 ohm (Bag 5), Located above the 1.5K resistor in the 'Audio Pre-Amp'.
____1 - 1.5K (Bag 6), Located above and between the .047 capacitors to the left of the Audio Pre-Amp.
____1 - 5.6K (Bag 6), Located above the 2N3904 on the right.

Solder

____1 - 39 ohm (Bag 5), Located above the 330mfd electrolytic.
____1 - 220 ohm (Bag 6), Located on the right of the 39 ohm resistor.
____1 - 2.2 ohm (Bag 6), Located below the 220 ohm resistor.
____1 - 1 ohm (Bag 6), Located below the 1mfd cap on the far right of the section near the Speaker box.
____2 - 10 ohm, 1 Watt (Bag 5), Located above the 9779 Audio Amp IC. First, install one on top of the board as shown in the picture below. The second one is tack soldered below the board in parallel with the 10 ohm above the board as shown in the second picture below.

Solder

Solder the second 10 ohm resistor as shown below:

Solder

Capacitors:

____3 - .047 (Bag 4) (or 2 in Bag 5 and one in Bag 4), Located to the left of the text "Audio Pre-Amp". Orange colored, small square, leads flared out, labeled "473, C1J". Some kits may have disc ceramic capacitors marked ".047". The third .047 goes next to the 2N3904 footprint where a .1 capacitor is changed to a .047 as shown in the picture. Note yellow arrow and yellow text ".047".
____4 - 10 mfd Tantalum, 3 pin (Bag 4), The center pin is positive, two outer ones are ground, this part is used in automatic insertion PCB work so that it never gets put in wrong. Orange colored, with three short pins. Two are located near the 2N3904, one above and one below. Other two are located near the box labeled "Audio Control", one above and one to the right.
____1 - 2.2mfd Electrolytic (Bag 4), Note that the negative (-) side of part is marked. The + (Plus) side is marked on the silkscreen. It is located above and left of the 2N3904 in the 'Audio Pre-Amp'.
____1 - 100mfd Electrolytic (Bag 6), Located below the 9779 Audio Amp IC. It is replacing a 2.2mfd Electrolytic to improve the audio response. Note yellow arrow and yellow text 100mfd.
____2 - 330mfd Electrolytic (Bag 4), Note: - (Minus) is marked on the part, and the + (Positive) is marked on the board. One is above the box labeled "Audio Control". The second one is to the right of the 9779 Audio Amp IC.
____1 - 100pf NPO (Bag 3), Orange color, short leads flared out, labeled "101". Located in the middle of the board above the 330mfd Electrolytic.
____1 - 1mfd Film (Bag 6), Located next to the box labeled "Speaker". Large red rectangle, labeled "105".

Solder

Other Parts:

____1 - 2N3904 transistor (Bag 4), Note flat on part and match to the flat on the footprint.

Solder

____1 - 9779 Audio Amplifier and Heat Sink(Bag 6), Be careful mounting on the board so that all five pins go into the PCB. Sometimes the pins may be bent out of place from shipping. Note mounting picture below.

Be careful mounting the heat sink, it is a slip on part. Use a small screwdriver to hold back the clip to help it slip on easily. Best to put the heatsink on the IC before soldering to the PCB.

Some kits may have a LM383 or a house numbered part "9779", which are identical both in dimensions and electrical properties.

Solder

Audio Control Potentiometer

There is a place below and left of the Audio Control Square that has ten holes that will accommodate most PCB mount potentiometers.

The pot supplied with the kit has five pins and matches the five holes in the forward part of the square. The pins are slipped through the holes and then soldered. Connection wires are run from the pins labeled "1", and "2" and run to the "Audio Control" square. The Grounds are connected through the ground plane.

Wiring the Potentiometer

Note: The following wiring instructions should be done with all boards built before year 2020. The audio increases nicely from low to high with this modification.

____1 - 10K Potentiometer (Bag 6), A small white pot labeled 10K in the upper left hand corner on the top.
____Use a 1 1/2" jumper wire and connect the the hole labeled "1" to the hole in the "Audio Control" square labeled "2".
____Use a 1 1/2" jumper wire and connect the hole labeled "2" in the "Audio Control" square labeled "1".

S-Meter

____The resistors that are used at M1 and M2, to the left and above the S-Meter Square at the AGC Detector (Picture), are set up to use a 50uA meter. (Picture)
____If the plastic S-Meter was ordered with the kit, make sure you put a 22K resistor at "Mtr1" for proper operation of the meter. (This resistor with the S-Meter.)

You can use any meter with a value between 50uA to 250uA, by changing the M1 and M2 resistors. Values for different meters are given in the S-Meter page. Circuit theory is included to help you properly set up the meter any way you like.

____The S-Meter, if board mounted, is glued to the top or bottom of the board where the text "Audio Amplifier" and the "Designed by...." is located at the bottom right of the board.

Silicon Rubber Sealant was used to secure the S-Meter on all the prototypes, and allows you to pull the meter off the board if you transfer the receiver to a case, where you will be mounting the S-Meter on a front panel. Picture

____Solder a wire from the + hole in the S-Meter square on the PCB to the + connection on the S-Meter.
____Solder a wire from the - hole in the S-Meter square on the PCB to the - connection on the S-Meter. Picture

Double Checking Your Work

____Place the PCB in front of a bright light. If you see light shining through any of the soldering holes, you missed a solder connection.
____Check the dot on the MOSFET.
____Check the flat on the 2N3904.
____Check the blue bands on the four HP5082 diodes.
____Check the dot on the Minicircuits T1-1T transformer.
____Check the flat on the LED and make sure it fits the flat on the footprint.
____Did you remember to turn the "Gain Adjust" (100K Black or Blue trim pot) all the way counterclockwise?
____Make sure the 2.2mfd, and two 330mfd Electrolytics are mounted correctly, located right next to the regulator, and at the Audio Amplifier.

If you have already tested Board 1, go to Mounting/Testing Board 2.

Mounting/Testing Board 1

Mounting/Testing Board 2

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Last Update: 3/24/2021
Web Author: David White, WN5Y Free Website Translator