Tecsun 2P3 AM Radio Receiver Kit - DIY for Enthusiasts, Built it into a radio case !

This was a very enjoyable kit to make and the completed unit works well. For those that have a transistor beta (hFE) tester, a voltmeter, some spare resistors, and a breadboard, you might want to make the following changes to the build procedures: Measure hFE of each S9018 transistor and order them from highest to lowest and then assign them to the circuit as follows (my hFE examples in brackets). Q1 - highest hFE (104) Q2 - mid-level hFE (102) Q3 - lowest hFE (97) Note that the provided kit bias resistors seem to assume hFE 100 so you will know to modify the resistors if you measure far off that nominal value (100). Build and test each section as you go - starting from the audio amplifier, then second IF amp./detector (Q3), then first IF amp. (Q2) then the Mixing circuit (Q1). Calculating modified bias resistors: ----------------------------------------- A. Calculate R2 Ve = 0.68 (given on schematic) hFE Q1 measured (e.g. 104) Ic = (0.6 + 0.3)/2 = 0.45 mA desired collector current. then R2 = (hFE1 * Ve) / (1 + hFE1) / Ic e.g. R2 = 104 * 0.68 / 105 / 0.45 = 1.50k ohms B. Calculate R10 Ve = 0.07 volts (given on schematic) hFE Q3 = 97 (measured) Ic = (1.0 + 0.5)/2 = 0.75 mA desired collector current. then R10 = (hFE3 * Ve) / (1 + hFE3) / Ic e.g. R10 = 97 * 0.07 / 98 / 0.75 * 1000 (mA/A) = 92.4 ohms C. Calculate R8 Vc16 = 1.853 volts (build and measure the diode voltage source from your kit) hFE Q3 = 97 measured Ic = 0.75 mA (same as step B.) then R8 = hFE3 * (Vc16 - 0.8) / Ic R8 = 97 * (1.853 - 0.8) / 0.75 = 136k ohms D. Calculate R6 Vc15 = 2.78 volts (capacitor voltage given on schematic) Vc2 = 1.6 volts (collector voltage given on schematic) Ic = (0.6+0.3)/2 = 0.45 mA (range given on schematic) then R6 = (Vc15 - Vc2) / Ic R6 = (2.78 - 1.6) / 0.45 = 2.6k ohms E. Calculate R1 Vc16 = 1.853 volts (build and measure the diode voltage source from your kit) hFE Q1 = 104 measured Ic = 0.45 mA (same as step A.) Vb = 1.3 volts (given on schematic) then R1 = hFE1 * (Vc16 - 1.3) / Ic R1 = 104 * (1.853 - 1.3) / 0.45 = 128k ohms The values of R5 and R7 were used unchanged (as they came in the kit) because their calculation is made more difficult by the circuit feedback. My circuit worked well even with hFE of Q2 (102) being slightly off the nominal value of 100.

マニュアルは、分かりやすく、完成して性能が良かったが、半年で選局ができなくなった。部品の品質に問題あり。

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A qualidade do produto é conforme as minhas expectativas.

Well thought out assembly instructions, require good soldering skills for small components