Wim Crystal set

Photo and Text information


My Crystal Set “Dutchie”


“The proof of a design is in its simplicity”


Being retired for about one year now, I found my way back into “the Basics of Radio” by reading the comments of the enthusiastic members of the “Crystal Set Radio Club” & “the Xtal Set Society”.


I tried to make myself a crystal radio just like I used to make them together with my father when I was a kid.


After experimenting a while I had a collection of radio parts on my desk that looked like a “spider” but that was slowly starting “to talk” to me…


From some cheap materials and a little plywood, I made a cabinet for the “spider” and with the help of a little oak coloured paint and a coating of transparent PU lacquer, I gave it an antique look.


The design is not at all new or very special, in fact the only unusual concept is a set of coils where the first, not tuned coil (antenna coil), has 4 taps and has a very small diameter (15 mm) compared to the second one, the tuned detector coil (70 mm). This concept causes the coupling between the coils to be almost purely inductive.


Some coil data:


Coil #1: 80 turns of copperwire 0,35 mm diameter on 15mm PVC pipe,

   taps every 20 turns.

(total 48 microHenry, taps at resp. 4, 17, and 33 microHenry).

Coil #2: 54 turns of copperwire 0,6 mm diameter on 70mm PVC pipe,

   1 tap after 11,5 turns.

(total 209 microHenry, tap at 17,2 microHenry).


I built a germanium diode (AA112) inside the cabinet, more or less as a reference detector, but this diode can be switched off and an external detector can be connected to 2 terminals on the front (this makes experimenting a lot easier).


The capacitor (condenser…) is a foil type cap, of 500pf (I could not find an aircapacitor in the local radio stores). In my junkbox I found a vernierdrive knob 1:3,5 to make tuning easier.


The phones terminal can be shunted by a (home made) resistor to be able to connect crystal earplugs.


The set performs exceptionally well; the selectivity can be adjusted by changing the degree of coupling between the antenna and the detector circuit.

May the best design win, good luck to all fellow contestants,

Wim van Leeuwen

(Dutch Ham: PA3CAY, Yahoo Crystal Set Radio Club: Coherer2000)