Solar powered AM tube radio


For this radio I had set myself a few goals.
Not only had this radio to be a tube radio it had to be also solar powered. I managed to make both goals and ended up with a very nice looking radio. It preforms better then i expected.

Side view Making a radio the old fashion way means also that the case needs to have lots of free space. The coils, the tuning capacitor, the speaker and even the choice of materials have a huge impact on the performance. Large metal objects close to the coils is a no go. You have to take care how the wiring is laid out and where to implement shields and filters.

Top view As you can see the top side of the case is largely empty. Here is only the large spiderweb coil, the tuning capacitor and the gearing to ease the tuning. The capacitor had already a venier drive with a 2.5:1 ratio. I made a small gearbox to reduce the ratio further down to 20:1. This give me a nice slow tuning over the whole spread.

Schematic The schema i used follow mostly the design of Dave Schmarder who has a great site about radio's
When switch S1 is in the OFF position then the solar cells will charge a 1.5V rechargeable battery and two 9V rechargeable batteries. The radio is able to run directly from the solar panels however this isn't really practical. First you must be absolutly sure that the filament isn't getting more then 1.2V. More voltage then this will shorten the life of the tube or it even can damage it. The anode voltage will vary to much if even a small cloud is passing the sun. This will result in fading sounds and frequenty shifts.