The Mystery Plus Crystal Set

By "Proton"
Published in "The Sunday Mail", Brisbane, Australia 16 April 1933

Those readers who study our radio-query columns will no doubt have noted the large number of readers who have thrown down the gauntlet by asking me to improve the mystery crystal set. In a weak moment I accepted the challenge, and promised to see about it. This promise was made about three months ago, and last week a reader wrote in and frankly said, "How about it?".

Well, I have tried out about 10 Mystery variations since the original was first described and could not find anything better. On top of this, many interested readers sent along their ideas and suggestions, and still I was not satisfied that any improvement had been made.

Last week, however, the inevitable improvement came along- not from me, but from a man whom I do not even know, who told me how he had bettered that "cove" Proton's circuit. Of course, I was all attention and later tried his scheme out.

Apart from the hard job I had to wind the coil, I was delighted and surprised to find whan an improvement had been made.

Now the Mystery Plus from a volume aspect is about equal to the original Mystery, but the extra coil certainly does increase the selectivity to a most remarkable degree, and I venture to say that, with this new version, there should not be a suburb in and around Brisbane, that will not tune in at least three of the local stations without interference. In most suburbs all four stations will be tuned in quite free of interference, but I am aware that in a few districts one station cannot be tuned in at all on a crystal set.

The variation is really as very small one and those readers who own Mystery Crystal sets will not have much trouble in altering their sets to the Mystery Plus: because the Plus is only something that other Mysteries have not got - a coil.

Mystery Plus rystal Set circuit diagram
The Mystery Plus crystal set schematic

Here are the components that you will acquire to construct the set:

1 One bakelite panel 9 by 7 inches
2 One wooden baseboard 9 to 7 by 1/2 inch
3 One .0003 µF variable condenser
4 One 3" plain dial
5 One glass enclosed crystal detector
6 One .001 mfd fixed condenser
7 One 3 1/2" inch length of 3" diameter tubing
8 One 1/4lb reel of 24 gauge D.S.C wire
9 One piece of empire cloth, 10 by 1 inches wide
10 Four N.P. terminals
11 Solder and a coil of hook-up wire

Construction Of Set

The construction of the receiver itself is quite straightforward. However, the coil is a little more difficult than usual, but I am sure that, if care is taken, very little trouble will be encountered.

Firstly, wind 12 turns of 24 gauge D.S.C wire on one end of the former, and, without breaking wire, stop winding and punch two holes in the former and thread the end of the 30 gauge through these two holes and make it secure.

Then continue the winding with both the 30 gauge and the 24 gauge wire until 23 turns have been wound on, and then you will have a turn of 30 gauge wire between each turn of 24 gauge wire.

Now that you have 36 turns of 24 gauge and 25 turns of 30 gauge wire wound on, stop winding and without breaking the 24 gauge, break the 30 gauge.

Then punch two holes in the former at the spot, where the 25th turn of the 30 gauge wire ends, and thread the 30 gauge trough these to make it secure.

Now continue winding the 24 gauge wire for another nine turns.

Now over the centre of the dual winding wind the empire cloth and secure it around the former tightly with seccotine at the overlap of the cloth. Over the top of this strip of empire cloth wind 15 turns of 24 gauge wire and secure the ends by threading them thorough the cloth.

The coil is then completed.

Now that you have completed the coil commence to mount the other component. The .0003 µF turning condenser should be mounted in the centre of the panel, with the crystal detector in a horizontal along the top. The aerial and earth terminals are mounted on the left hand side of the panel, and the phone terminals are mounted on the right hand side of the panel. The panel should then be screwed to the baseboard, and the coil mounted vertically behind the .003 µF turning condenser, and the .001µF fixed phone condenser is mounted across the output terminals.

Care Necessary With Leads

When you have every thing in position commence wiring up from the diagram which should make everything quite clear. Care however, should be taken with the six leads from the coils, for if by mistake these should become reversed, the receiver will not operate successfully.

This receiver will be excellent to try out as an experiment over the Easter holidays, for all those crystal set enthusiasts who have built up Mystery crystal sets in their original forms will have very little difficulty in making the change over. Those readers who are trying out the Mystery for the first time will be surprised at its sensitivity and selectivity.