Gachapon capsule 3 tubes reflex super het
Completed   Sep. 2004


   Size : 2.8"x2.6"x2.6"(except protrusion of knob)         


Features :                                                                                                 
*Tube portable radio made into gachapon capsule.                             
*About the same sensitivity with standard 4-tubes portable super het.
  And loud speaker is also built in.                                                  
*Comprise minimum number of necessary and easy obtainable parts.  

without upper cover

カプセルを外した状態 without capsule
この状態で音が出ます。 It operates completely at this state

使用球    : 5678 x3                                                                           
Tube line up : 5678 x3                                                                            

回路構成:周波数変換 中間周波増幅  検波     電圧増幅    電力増幅
          5678     5678    ダイオード   5678      5678

Block diagram: Converter  IF-AMP      2nd-Detector   AF-AMP       Power AMP
                       5678         5678             diode          5678             5678
                                   *AF and IF are amplified in 1 tube using reflex circuit




Motive for making this radio and policies :
One day, I went to a toy shop with my daughter(8 years old at that time), and I caught sight of Gachapon machine.
I           "It will be interesting to build radio into Gachapon capsule."
daughter "Well... It may be interesting. But Can you really make such a radio?"
I           "O....Of course, ... I can!"

Gachapon machines are small vending machines of toys. I don't know their formal name, they are called Gachapon or Gachagacha.
In Japanese cities, they can be seen every where kids go.
A toy is contained in capsule. To buy it, slot in 1 or 2 coins and turn handle of  Gachapon machines, and then a capsule pop out.
But kids who buy it never know what toy is contained in the capsule until it pop out. It has some factor of gamble.

And it started. I said so, I must complete this radio, if not, It will be beneath my dignity as father.  
 I planned with the policies listed below.
      1,Make it will have enough performance for practical use, with loud speaker.
      2,To be a radio of "Musenka" , I planned to use minimum number of necessary and easy obtainable parts.


*Schematic is only a reference and can be use freely  But I  can't be responsible for any result.

 回路は 「MT管式レフレックス3球スーパ」や「ST管式2球スーパ」等と同じ構成ですが、できるだけ入手容易な部品を使用し、かつ部品点数も最低限とするため、かなり割り切った回路になっています。

About schematic:
Schematic diagram is about the same with "3-mT tubes reflex super het" or "2-ST tubes super het". But to make with minimum number of necessary and easy obtainable parts, I gave a clear-cut solution.
I used 5678 tubes only Because I thought 5678 is easiest to obtain in this kinds of sub-mini type battery tubes. I don't want to use semiconductor diode in my tube portable radio.
But to get practical performance with only 3-pentode, I have no other way except using semiconductor diode. And I made a compromise.
Frequency changer is pentode converter with 5678. Its circuit diagram is almost the same with other radios posted on this web site.
And I can avoid using converter tube like 1V6 which is rather difficult to obtain (in Japan).
Same as "2-tubes reflex super-het using Russian sub-mini tubes" , two IFTs are both single tuned type. I use one transistor-radio-IFT for each of them. Coil specifications of IFTs are also the same with this radio.
Usually AF load of reflex circuit is choke coil. But I substitute resistor of volume control for choke coil. Because this choke coil is rather expensive and occupy many space. Plate voltage of IF/AF-AMP become lower with this arrangement. But Contrary to general belief, there are almost no problem. I think one of the reason is high voltage (equal to B-voltage)of screen grid.
 I could obtain main electronic parts except tubes, output trans, speaker are get from one 100Yen radio once sold (in Japan). Now 100Yen radio is not sold in actuality but there are cheep pocket AM radio having 5 transistor superhet circuit. Main electronic parts are also obtained from such a radio. Thus, It became suitable circuit as radio of "Musenka".   

     電池: ・A電池:単4x1 1.5V
          ・B電池:23A 12Vx4個 48V
          Batteries requirement:
*A-batteries : AAA-cell x 1  1.5V
                      *B-batteries : 23A   12Vx4   48V

          Parts:       *Main parts except tubes, output trans and speaker
                           are parts are taken out from 100Yen radio.
                         *Output transformer--Remake of ST-30 (equivalent type)
                         *Speaker is out from small speaker box of 100Yen shop. 

      外装   :ガチャポンのカプセル(直径約65mmのもの)を使用

          Casing      : Using Gachapon capsule (diameter of about 65mm)

         シャーシ :金属製のシャーシはなし。ユニバーサルプリント基板を使用
           Chassis    : Using PWB, has no metal chassis

          つまみ類 :100円ラジオのもの
           Knobs       :Knobs of 100Yen radio.

外装、構造 :

Casing and mechanical structure:    
All parts including loud speaker and batteries holder are fixed to resin (acryl) plate and form a "circuit unit". Most of electronic parts are fixed onto universal type PWB of half circle shape and this PWB is fixed to resin plate.
 Loud speaker is fixed under the PWB upward. This arrangement is reverse to usual arrangement. But I had no other way to build in loud speaker of this size (about 2" in diameter) in Gachapon capsule.  
 I decided arrangement of A and B batteries with an great effort. I aimed at batteries holder with simple structure. But it had become a batteries holder with very complex structure.  
The "circuit unit" is only "contained" in Gachapon capsule, is not fixed to it.

部品が取り付けられる「樹脂板」 樹脂板上に取りつけられた電池ホルダ 完成した「回路ユニット」
"Resin plate" to which all parts are fixed.  Batteries holder on "Resin plate" Completed "Circuit unit"

   組立図 assembly drawing

性能、他  :

Performance and others :
 All stations within about 30 miles can be received with built-in stick antenna in my home (ferroconcrete structure). And at night some distant station can be received. Sensitivity is unexpectedly good. But sound tend to distort when input signal is large, because volume control is put after AF-AMP. And because of improper arrangement of speaker, volume of sound is not so large. But I think it will be sufficient volume level, when listened by 1 or 2 person.
I wanted to use AA size cell as a A-battery, but I could arrange only AAA size cell. So, life of A-battery is about 4-hours with alkaline type cell.   
 Appearance of this radio remind me of head of some robot in SF movie or TV, like "Robbiy" in "FORBIDDEN PLANET". It will be suitable as ornament on desk..
Execution as radio of "Musenka": I could obtain most of its parts except tubes and output tras at 100Yen shop or DIY shop. And case is utilizing of waste material. So, all parts except tubes could be obtained at price of  about 800Yen (about US$ 7.3) .  This price was the price in case of using 100Yen radio that is not available in actuality now. But now we can buy 5 transistor superhet at price of about 800Yen (US$ 7.3) at some DIY shop in Japan. And with this 5 transistor superhet, all parts except tubes are obtained at price of 1300Yen (US$ 11.8).
5678 tube is about US$3.0/pcs at mail order firm in U.S.A. But if We buy 5678 only 3pcs, postage (to Japan) will be comparatively expensive. Used 5678 tubes are sometimes available at price of 100 or 200Yen also in Japan. They were used in military radio communicators.