631
Item nr.
| Production | The Netherlands, 2026. |
|---|---|
| Bands | MW (540-1600kHz). |
| Semi- conductors | TA7642, BC337. |
| Cabinet | Plastic. Size 23.5x23.5x11cm. Weight 1.47kg. |
| Power | Batt 1.5V (0.4 - 0.9mA). |
| Documents | Schema. |
It has biastonic volume control, a TA7642 tuner, and BC337 as amplifier. I received Radio Paradijs, Sitar, MCB, BBC5, and Caroline. If you want to build such a piece, mind the value of R2, perhaps some experimenting is useful. The value of 3k2 is good for receiving strong stations; to make the set more sensitive, use a smaller value. The capacitor on the primary of the output transformer reduces the high to avoid shrill sound. Its best value depends on the load impedance formed by the transformer and the speaker. In my set, the load is about 10kOhm and the cap is 10nF, giving RC product 0.1ms, and cutoff 1700Hz.
| Obtained | 6/2026 from home built. |
|---|---|
| Condition | 8. |
| Value (est.) | 3,3€. |
| Sound sample | PLAY SOUND No milk today. |
was picked up from the Recycle Store for 1.5€. Unfortunately, the type sticker misses some digits. 
The speaker came with a most curious plug (right). It was discussed at Melius Club. The lack of a proper type number seems to indicate that these were not sold separately, but only as part of a set. 
The inside view is of course dominated by the AD8080/M4 loudspeaker. The top right has the AA battery. The bottom right has the smoothing cap, power switch and the biastonic volume control. The bottom left has the tuner and (below the tuning cap) the ferrite rod antenna. The top left shows the Output Transformer with the BC337 amplifier soldered to it. Now for some measurements, taken with 1.52V battery voltage. The drop over R2 (of 3k2) is 603mV, indicating a DC current of 188µA. The DC resistance of the Output Transformer primary is 488Ω. The transformer has voltage ratio about 50, so impedance ratio 2500, and with a 4Ω speaker this means a primary load impedance of 10kΩ. The bias resistor R3 has a fixed and variable part and measures (in MIN position/in MAX position) 928 / 332kΩ. The voltage over the transformer measures 70/188mV, indicating a collector current of 143/385µA. The total current draw from the battery is 321/588µA.
What about the sound? Of course, this set always plays at a very moderate volume. But in MIN position, the sound is already loud enough for background listening in my garden when it is quiet. Sometimes I even reduce the volume further by primitive methods like slightly mistuning. When there is more background noise, or a popular song is played, I can increase the volume satisfactorily. So, though I had not expected this to be possible, I have a nicely working radio, taking significantly less energy than my Garden Radio, just 0.5 to 0.9mW.