HX108-2 7 Transistor AM Radio Kit - Audio Sections

K7QO HX108-2 AM Receiver: Theory and Construction - Part 03 HX108-2 Audio Sections

Schematic of the components of the AUDIO sections to be  installed on the PCB (Yellow highlight)

Figure 1: Part 3 AUDIO sections

Power supply connections installed in Part 1 are in the Green highlight. I also highlight on the parts list the items  I remove from the cardboard strips to show that they were installed

Figure 2: Wiring Audio Sections Complete

After PCB components were soldered (including the two audio transformers) I soldered the two yellow wires supplied to the PCB only, then I added the two yellow jumpers to connect the speaker.

Test Data Measurements - Part 3 Audio Sections

1. Current measured at TP5 = 12.2 mA (4-10 mA -suggested)
2. Current measured at TP4 = 4.7 mA (2~5 mA -suggested)

Current is 2.2 mA higher at TP5 than suggested maximum value.

Current at TP4 is just below the suggested maximum value.

I will solder bridge the traces at TP5 and TP4

I will cautiously continue to Part 5 Band Pass and Demodulator Section

In Part 4 Chuck Adams K7QO Analyses the circuit for the excessively high current in the Audio sections of his build.

Figure 3: Top side PCB with Audio Sections Installed

In Figure 3 I show the Audio sections installed. Please note I have marked over the Chinese character for B2, B3, B4 and B5 with the initial for the color painted on the core slug,  Also note the line on the volume control thumbwheel. In the 7 O'clock position the switch K is OFF.

73, AB1OP Ralph

HX108-2 7 Transistor AM Radio Kit - Power Supply 

Links:

• HX108-2 English Documentation - Improved 
• YouTube Page of Chuck Adams, K7QO

On K7QO YouTube page scroll down to the heading: 
Chuck Adams RF Receiver Course on YouTube
find links: 
K7QO HX108-2 AM Receiver: Theory and Construction - Part 01 to 
K7QO HX108-2 AM Receiver: Theory and Construction - Part 09. 
If you watch and follow along "You might learn something" as Chuck K7QO said.

Part 01  HX108-2 Introduction and Power Supply 

Unboxing and parts inventory - Kit has all discrete electronic components, to be mounted on a thru hole PCB. No IC's, no SMT/SMD parts, but also no assembly instructions. (Not your Dad's Heathkit...) 

You do get a single sheet that combines the schematic, parts list, PCB diagram, resistor color code, capacitor code, transistor pinout, specifications and soldering instructions that are all in Chinese. 

The schematic has a few errors and there have been instances where the transistors were substituted with other transistors having a different pinout.

For all these reason this kit is not recommended for a novice kit builder without an Elmer.  

The Chinese documentation included in my kit purchased in March 2019 was dated 2018.8.6 The PCB is marked 20110518 which I assume is the PCB version date. 

Part 1- Power Supply

 Got the schematic with the power supply circuit highlighted.  I also place the small electronic components in the edge of strips of corrugated cardboard that I pasted a section from a copy of the parts list. Idea was from Randy - K7AGE from one of his YouTube Videos.

A cluttered bench is a happy bench

 I started assembly of the case. I installed the speaker, battery terminals and the front faceplate. I had to use super glue to keep the long spring wire terminal in its slot when the AA cells are put in.
I also placed the thumbwheel and screw on the shaft of the volume control W and marked a line that would point to 7 o'clock position when K is off (open).

On the PCB I used a 15W soldering iron, 60/40 solder and a liquid rosin flux pen. Soldering to the PCB was good with only a few joints requiring reflow.  One difficultly was the supplied wire for the power leads were smaller than 24 gauge (smallest setting on my wire stripper). I used an X-acto knife to trim the insulation back so I would use jumper leads between the case and the wire leads soldered to the PCB.

Test Data Measurements: 

• Voltage across battery terminals = 3.2Vdc
• Voltage from anode D1 to Ground = 1.45Vdc K=on / 0.0Vdc K=off
• Voltage from anode D2 to Ground = 0.72Vdc K=on / 0.0Vdc K=off 

Test data measured was the expected results. Part 1 of the build was successfully completed.
In Part 3 we will solder the components that comprise the AUDIO sections.

(Part 2, Chuck Adams K7QO suggests some of the test equipment you may wish to use.  Including some cheap Chinese kits available of eBay.)

73, AB1OP Ralph

My DIY DVM Bench Stand

I was cleaning off the work bench in preparation of a new project.  I always wanted to be able to prop up my DVM to a more comfortable viewing angle while seated. When using a temporary prop the DVM would slide off as I'm turning the function/range switch or adjusting the cables.

My design goals:

1. Cheap method to tilt the DVM to about 45 degrees
2. Must be stable enough to turn the selection switch without coming off stand
3. Simple to build with my tools
4. Materials at hand or readily available
5. Cheap (can never be too Cheap)

Final Product:

Digital Multimeter Stand

 

All Butt joint construction

Materials:

• 1"x2" (0.75"x1.50") Strapping / Furring strip 9.5" long
• 4 Wood fasteners (I used 1.5" drywall screws)
• Wood Glue

My Tools:

• Saw (I used a jig saw, a hand saw would work, a powered miter saw would be quickest)
• Square with ruler marks
• Pencil
• Drill/Driver
• A Twist drill for pilot holes
• Phillips Bit
• Coarse/Medium Sandpaper

Directions:

1. Measure and cut TWO (2) 3" pieces from the 9.5" wood strip. You should have about 3.25" remaining from wood strip. (exact measurements not critical)
2. Take the 3" pieces butt together to form the bottom and the front tail rest (see second picture) Locate and drill pilot holes (if screwing) Apply glue to the end grain of bottom piece and fasten. Wipe off excess glue.
3. The other end of the bottom piece is butted to the long back headrest, drill, glue, fasten and wipe as before. (see second picture) 
4. Sand wood edges with sandpaper to prevent splinters. Sand a bevel in the top front of the headrest (optional) to fit the lean of the DVM. 
5. Apply finish (optional) and enjoy!