What does the project present?
This vintage DIY electronic kit was launched on the market in 1981 and was an assembly loved by amateur electronics because of its simplicity and enough power for an apartment.
Power transistors 2N3055 they can be easily purchased as well as the other components. The article also specifies the values of recent equivalent components.
The vintage DIY electronic kit presented is practically a 10W mono amplifier. Thus, in order to have a stereo sound, it is recommended to use two such kits.
How does the assembly work?
An audio amplifier is an electronic assembly, which receives an electrical signal that it reproduces (in terms of frequency), but on a larger scale - so with a power gain (provided by a power take-off from direct current source). The signal frequency is considered in the audio field. The signal can be taken from the radio, mp3 player, PC or laptop and finally amplified on the speaker.
Group R1, C1 ensures only the input of the alternative component. Transistor T1 shows a good signal reception, due to the increased input impedance by connecting capacitor C4.
Diodes D1 and D2 achieve an initial opening voltage for the doublet groups T4 - T5, respectively T2 - T3, which conduct an alternation of the signal, in turn, being then successively blocked. Through the capacitor C6 is separated the direct component due to the direct current source, from the useful signal that is applied on the speaker. The resistor R11 (reaction) serves to control the amplitude of the signal as well as the widening of the frequency band in which the amplifier activates.
In the series production of this DIY electronic kit, they were used three types of leaflets having similar content (one white and two orange). Two of the leaflets had the number 8109, and one 7904. The latter was called "10W Amps".
Technical characteristics of the assembly
- Supply voltage: 20 Vdc.
- Maximum current absorbed: 1A
- Speaker impedance: 4-8 Ohm (minimum power 10W on 4 Ohm)
- Input signal level: 1 - 1.5V
List of required components (with recent equivalents):
- T1 - transistor BC 172 or BC547C
- T2 - transistor SPD1 - BD 136, BD 138, BD 140
- T4 - SND1 transistor - BD 135, BD 137, BD 139
- T3, T5 - transistors SN100 - 2N3055, SDT9301 or 2N3773
- D1, D2 - diode - 1N4001 and 1N4007
- R1 - resistor 1.5 KOhm (min. 0.25W)
- R2 - resistor 5.6 KOhm (min. 0.25W)
- R3 - 680 Ohm resistor (min. 0.25W)
- R4 - resistor 18 KOhm, 22 KOhm, 27 KOhm (min. 0.25W)
- R5 - resistor 1.2 KOhm (min. 0.25W)
- R6 - resistor 3.9 KOhm (min. 0.25W)
- R7, R8 - 470 Ohm resistors (min. 0.25W)
- R9, R10 - 0.47 Ohm resistors (min. 2W)
- R11 - resistor 82 KOhm (min. 0.25W)
- P1 - 250 Ohm semi-adjustable potentiometer or 50K logarithmic potentiometer
- C1 - capacitor 22uF / 25V
- C2 - capacitor 100uF / 25V
- C3 - 220pF / 25V or 339pF / 25V capacitor
- C4 - 100pF / 25V capacitor
- C5 - capacitor 10uF / 6.3V
- C6 - 1000uF / 25V or 6800uF / 25V capacitor (if the value of the capacitor on the output is small only the low frequencies will be attenuated)
- Two radiators for T3 and T5 (see details below)
- Printed wiring or breadboard test board
- Tin or connecting threads
It is recomended that after assembly, before starting to make adjustments and tests, the first measurements should be made with the amplifier without load at input and output (ie without speaker and signal at input).
Also, do not immediately connect the amplifier to the audio signal source. Check that no capacitor on the input is short so as not to risk damage to the signal source (sound card).
The size for the radiators required for T3 and T5 is not specified anywhere in the leaflet. So, we recommend the use of radiators with a minimum size of 16 x 38 x 16 mm3. see here how to calculate the size of the radiator depending on the power dissipated by the transistor.
For a better understanding of the operation of the circuit we will need electronic scheme presented below:
In order to carry out this project in our own laboratory, we will also need printed wiring PCB layout From lower:
Many of you are probably wondering how this DIY electronic kit was packaged or distributed. Below I have attached some pictures with packaged product (new). Thanks sir. Marius Balauta! It is practically the first variant sold on the market out of the three mentioned above.
The image below shows the electronic kit in another variant, having the same prospectus number (8109).
In order to have a clearer view on the components used in the realization of this project, we have attached the picture below. Thank you sir. Adrian Biruescu!