Three Transistor Radio Parts List
The cost of components and parts is forever increasing, and therefore it is logical to recycle some of the parts you may already have. Whilst components such as the loudspeaker and variable capacitor may not be so critical, the fixed ceramic disc capacitors are. In particular, C1, C2, and C3 maintain the bandwidth of the high-gain amplifier. The values shown fix it to receive signals within the medium wave (MW) band. Changing these will change the characteristics of the amplifier stages.
Capacitors
The value of capacitor C1 at the base input of Q1 is extremely critical and must be 47 pF. The ceramic disc marking will be "47". Capacitor C2 is also critical as it ensures that the transistor amplifies signals in the MW band. The marking on the capacitor should be "104" which represents 100000 pF, which is 100 nF, or 0.1 uF.
Capacitor C3 (marking 104J) performs a number of tasks. Firstly, it earths any radio frequency (RF) signals that may have made it this far. At this final stage, we do not require any RF, and transistor Q3 amplifies only audio frequency (AF). It also removes some of that sharp high frequency hiss but leaves the bass, which makes it sound extremely nice if you had a good pair of headphones.
Volume Control
The volume control is a 10 kΩ logarithmic potentiometer. It is very rough and ready because on one side, you get a lower volume without the treble, thanks to C3, and on the other end, you get a high volume with full treble.
This radio does not have an automatic gain control (AGC) and you get to hear the signal exactly as it arrives. This means that the signal from some of the distant radio stations will be weak, and you will need to have the volume to a mid level. However, tuning to a nearby station with a strong signal will produce extremely loud audio and you will need to turn the volume to a low level. When tuning through stations, keep the volume low, and increase it gradually after you have selected the station.
Components
| Quantity | Component | Value |
| 3 | Transistors Q1, Q2, Q3 | MPSA13 |
| 1 | C1 | 47 pF |
| 1 | C2 | 0.1 µF |
| 1 | C3 | 0.1 µF |
| 1 | VC | 300 pF |
| 2 | Electrolytic Caps | 1 µF |
| 2 | Resistors | 4.7 kΩ |
| 1 | Resistor | 1 MΩ |
| 1 | Resistor | 6.8 MΩ |
| 1 | Resistor | 10 MΩ |
| 1 | Resistor | 10 Ω |
| 1 | Potentiometer (Log) | 10 kΩ |
| 1 | Transformer | LT700 |
| 1 | Loudspeaker | 8 Ω |
| 1 | Slide Switch | 2 Poles |
| 17 | ½-inch Brass Screws | No. 6 |
| 17 | Brass Screw Cups | No. 6 |
| 1 | 1 metre | CAT 5 UTP Cable |
| 1 | Ferrite Rod | 10 mm Diametre |
| 1 | Aerial | Telescopic Type |
| 1 | Baseboard | 65 mm × 200 mm × 15 mm |
| 1 | Battery | 9 V |
| 1 | Battery Connector | For 9 V PP3 Battery |
Tools
| Tool | Description |
| Soldering Iron | 12-watts |
| Solder | Omega Type |
| Minature Drill | Crafts type |
| Drill | 1 mm Dia |
| Hot Glue Gun | Minature |
| Glue Sticks | Clear Type |
| Punch / Nail | For Making Indentations |
| Small Hammer | Minature Type |
This Article Continues...
Three Transistor Radio - Whippersnapper 2Circuit Diagram
Ferrite Coil Antenna
Loudspeaker and Transformer
Variable Capacitor
Baseboard Layout
Parts List
Completed Build