Dave's #44 Crystal Set
Hi Friends. Sorry this one took so long in getting to my web site. I think that some of you may want to build this one. This is a more modest version of my #35 dx radio. #44 costs much less to build than the big ones. There are two parts to this radio. The Antenna Tuning Unit (ATU), which is pictured to the left. On the right is the Detector Unit (DU).
In normal use, the two coils are placed about 6 inches (15 cm) apart with the coils directly facing each other. The RF energy comes in from the antenna and is tuned with the pair of 365 pf capacitors. The basic method of tuning is as follows: If you want the highest selectivity, the capacitor in series with the antenna is kept at a minimum value (plates mostly unmeshed). The parallel capacitor is then used to peak the signal. Conversely, if you need more sensitivity, and give up some selectivity, turn the antenna capacitor towards maximum capacity. The two capacitors independently will give you the most control in your reception.
The DU has two controls, the main tuning and coupling. If you want maximum sensitivity, turn the coupling control towards maximum capacitance. Maximum selectivity is the opposite, minimum capacitance. The detector tuning control is always peaked to the desired station. It will take some practice to juggle all the controls, but the reception will be rewarding.
This radio uses 165/46 litz wire for the coils. This is a good all around wire with a good balance between price and performance. The capacitors are standard type 365 pf variables found sold by different online sellers. Increased performance will be realized if you use better capacitors, such as ones manufactured by Jackson Brothers.
The coupling capacitor can be a fixed 10 pf type or a trimmer capacitor. If you can find a shaft type capacitor, that will be better. Make sure you use an isolated shaft to the knob, otherwise the hand capacity effect will drive you verrückt. A 1N34A diode will work fine here, but a better diode to use is the FO-215 germanium type. The transformer is a Bogen offered by myself and others. Don't substitute this transformer for other speaker transformers. This one has a special high impedance tap not found on other transformers found in the US.
Of course, how you put it together is up to you. I used an oak base and Garolite® panels. It's ok if you copy how I did mine. I would be flattered, but other ideas are good too.
73 and good crystal DX. Dave - N2DS