Dave's #61 Crystal Radio
Have any of you actually read all my crystal set pages? Really? I hope you get better soon. :) Thanks for sticking with me. I appreciate the cards, letters, e-mail gifts and the large bandwidth numbers gathered by this web site.
I'm sure you won't be disappointed with this radio because I'm not. This is a dual tuned, single coil radio, with a coupling circuit that was first seen (by me) in an old Australian magazine article. The Aussies were makers of fine radios and their descendants still make nice sets.
The coupling circuit that I refer to is shown in my schematic below as the 27 pf fixed capacitor and the 27 mh choke. How did I come up with these values? I picked what I felt would work well for all around reception. The 27 mh chokes have been a regular component in my sets for a couple of years. The chokes that I use work very well. The capacitor is also from experience. It seemed that when I used the 7-45 trimmers, the value that worked the best seemed to be in the middle. I decided to make this a fixed capacitor in this radio.
The variables are the usual 365 pf capacitors that are available from just about everyone. The knobs I used were made by General Radio. They are a heavy knob that really gives the tuning a good feel.
The coil is made from 165/46 litz wire. This provides efficiencies that aren't available in magnet wire. However if the litz is just out of your budget, go with the magnet wire. 100/44 litz is a good in between wire that is easier on the wallet. The winding information is the same for this less expensive wire. I used a styrene coil form. If you have a scroll saw, you can lay one out and make it.
I added one of my famous brass link switches on the front panel so I could switch in a germanium diode instead of using the pyrite detector. A regular toggle or slide switch could have been used, but those would have ruined the look.
The terminals for antenna, ground and phones are brass thumb nuts.
As always, I really enjoy the look of brass hardware, and with the mahogany
box and black Garolite®, this project really stands out.
This radio works great. The litz coil makes this a standout, along with the capacitor / inductor network I added. The selectivity is reasonable and if you have strong local stations, a wave trap can be added.
Good DX! Dave - N2DS