Almost a Crystal Set

Updated May 17, 2013, see below.

I built this radio in July 1999 to send to Owen Pool, who has a great crystal radio website. He had some simple radios on his site and somehow we started corresponding. I put this radio together in about an hour. It is built on an old shingle, with a popsicle stick regeneration control and a toilet paper tube for a coil form.

The circuit differs from the simple regen I built for 40m in that it works on the AM broadcast band. It worked better with the tickler in the source circuit. Don't know why. The tickler is wound on a short piece of toilet paper tube glued to a popsicle stick. A screw near one end of the stick lets you swing it around to control proximity of the tickler to the main coil. The antenna is just a 6 foot piece of wire. Like the 40m set, you unplug the phones to turn it off. This radio also uses the DC resistance of the phones for the bias resistor, so you need to use real 2K phones. An alternative is to make a parallel combination of a 2K resistor and a high impedance crystal earphone. That works OK.

Construction of the "Almost a Crystal Set" relies heavily on hot-melt glue.

Schematic Diagram of the Receiver
Parts List:

C1 365pF variable
C2 .01uF 50V mono ceramic
Q1 MPF102
B1 9V
L1 100T #28 on a toilet paper tube
L2 10T on a 1/2 inch long piece of toilet paper tube.
HS1 2K ohm headphones
May 2013 Update

Well, I sent that radio to Owen, so I never really got a chance to mess with it to see what it could do. I built one for myself, but with a rotating tickler arrangement this time. Same basic thing, but the main coil was wound with 65 turns on a used salt box tube.

The 2013 version.
Because of the large inductor, I think, you don't need an antenna to pick up the local stations. The local stations aren't very interesting, however, so I set the goal to try and get good copy on a station in Santa Barbara, about 25 miles away. It doesn't come in very well here on my car radio, so I considered this a challenge. If I use station ground and a 25' wire for an antenna, and inductively couple to the main coil, I can just get the station at a usable volume. It's pretty hard to operate this thing because getting your hand near the coil detunes the radio, but it is possible to tune in the station you want.
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