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HRSA South East Queensland Group - Crystal Set Competition

The Mystery Crystal Set
constructed by Ray Creighton

Which won 1st prize for Best Reproduction Crystal Set and 3rd prize for Best Performance Crystal Set at the Historical Radio Society of Australia - South East Queensland Group - Crystal Set Competition held on March 19th 2000 at Malaney (Approx 100KM North of Brisbane) Queensland Australia.

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Click here to view Other Mystery Crystal Sets

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Construction details of this crystal set were first published in Our Wireless Circle section of The Sunday Mail newspaper in Brisbane on July 3rd 1932. It proved to be very popular with the readers and a second construction article was published on July 17th 1932 along with readers letters and questions, and another on April 16th 1933.

new34.gif - 195 Bytes Update 30 July 00 I have now found a article dated 16th April 1933 which is added to the bottom of this page. Almost every sunday during this period there have been letters and comments regarding the Mystery Crystal set in the Sunday Mail. When I get a chance I will continue researching the Brisbane Sunday Mail.

Parts to construct a crystal set were relatively cheap and construction fairly simple so they were very popular at this time for people living close to radio stations. Your local radio dealer could construct the mystery crystal set for approx. 25 to 30 shillings ($2.50 to $3.00). At this time a cheap 4 valve radio (Radiola Junior) cost 24 Pounds 10 shillings ($49.00) approx. 6 weeks wages for a radio service man.

In 1932 there were only 4 radio stations in Brisbane, 4QG, 4BC, 4BK, 4BH and radio broadcasting in Brisbane was only seven years old, at the time there were a total of 17 radio stations in Australia

This circuit is unusual due to the earth connection being on the secondary side of the coil and only the aerial being connected to the tuned primary of the coil.

Note: I used a Brach fixed crystal detector ( It is the orange fuse like device at the back of the crystal set ) instead of a cats whisker, square bus wire for the connections, and I made the base and panel from Jarrah a fine Western Australian timber.

Note: When constructing my Mystery Crystal Set I found I got best selectivity when my aerial was connected to the capacitor moving plates and bottom of the coil. aerial connection, this appears to be the opposite to the connections shown above. B.A. = Broad Aerial, S.A. = Sharp Aerial.

The three articles below are as they were published in 1932 and 1933 in Brisbane Australia.
(The articles below are as they were printed, so it is the wording of the 1930's.)

The Mystery Crystal Set
(by Proton.)
The Sunday Mail - Brisbane Australia July 3rd 1932

The Mystery crystal receiver is so called because I do not know just why it should be so good, and after trying it out for about a fortnight I am more amazed at the results than before. It is without a doubt the best crystal set that I have heard. Some of the Sunday Mail crystal receivers have attained Australia-wide fame, and it is quite a common occurrence to receive requests from readers in every State of the Commonwealth, asking for details of the new34.gif - 195 Bytes Improved Interstate Crystal Set or the new34.gif - 195 Bytes DX Crystal Set , but, this crystal set, to my mind, eclipses them all.

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When you look at the diagram you will note that it is quite a different arrangement from that which you normally see in crystal circuits, but nevertheless it is a simple crystal receiver that will cost only a few shillings, and sufficiently selective to separate all the local stations without any overlap, and bring them in with enough volume to make the reception enjoyable. As compared with the Improved Interstate, this set is definitely superior. It tunes in the B stations with greater ease and with more volume, while 4QG's volume will surprise you as it did me.

The coil, like the whole circuit, is a most unusual arrangement, consisting of two coils wound together, turn to turn on the one former. The aerial coil, which is tuned has two aerial points without any earth connection. The detection and output circuit is untuned, and has the receiver's earth connection, a very unusual arrangement.

The components necessary to build this freak crystal set are:

CONSTRUCTION OF SET The first constructional step is the winding of the coil. As this is a little unusual, I will endeavour to make it as simple as possible. Wind 12 turns of 24 gauge D.S.C wire on one end of the former, and, without breaking the wire, stop winding and punch two holes in the former, and thread the end of the 30 gauge wire through these holes to make it secure. Then continue the winding with both the 24 and 30 gauge wire so that, for the next 25 turns, the coil is so wound as to have a turn of the 30 gauge wire between each turn of 24 gauge wire. When 36 turns of 24 gauge wire, and 25 of the 30 gauge wire have been wound on, stop winding, and, without breaking the 24 gauge wire, break the 30 gauge wire, and secure it by punching two holes in the former and threading it through these. Now continue winding the 24 gauge wire for another 13 turns, and then securely fasten by punching a further two holes in the former, and the coil is complete.

The .005 mfd condenser is mounted on the centre of the panel, and the three inch dial is then fitted. The crystal detector is then mounted over the condenser, and the switch arm and the two studs is mounted under the condenser dial. The serial terminals are mounted on the left hand side of the panel along with the earth terminal, while the two phone terminals should be mounted on the right hand side of the panel. The coil is mounted on the baseboard directly behind the .0005 mfd variable condenser.

The wiring up of the receiver is a very easy matter, as will be seen from the diagram, but to avoid any misunderstanding it should be noted that the 50 turn coil of 24 gauge wire is the tuned aerial coil, while the 25 turn 30 gauge wire coil is untuned and connects to the crystal detector and phone circuit.

OPERATION OF THE RECEIVER The operation of this receiver is just as simple as the construction. The first point to note is that the switch and the two studs vary the selectivity, for when the switch arm is in contact with the stud S in the diagram, the set is very selective, and will tune in all four locals without any interference, but when the switch arm is in contact with stud B the receiver is much broader in its tuning and interference may occur, but the volume is greatly increased. The .0005 mfd condenser tunes in the various stations in the normal way. A point worthy of mention is the phone condenser. This condenser is usually omitted, but in this set it will be found to increase the volume quite considerably.

The Mystery crystal set is really a definite solution to the inexpensive crystal receiver selectivity problem and all readers who build up the set have an excellent receiver possessing excellent punch and selectivity.

The Mystery Crystal Set
(by Proton.)
The Sunday Mail - Brisbane Australia July 17th 1932

The Mystery crystal set has proved most popular with constructors and some of the reports are really amazing, as the one published below indicates. A number of readers have written in asking for an actual wiring diagram, and this week, in response to their request, I am giving these details. In order to make the construction more simple , I have shown how to construct the set without the switch and studs by using two aerial terminals instead. This does not affect the receiver's efficiency, but it makes it easier to construct for those who have not the necessary drills and dividers.

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Now for a few hints. Firstly, if you desire to get the best results, build the set up in the manner instructed. Something else might work just as well, and on the other hand it might not, and everyone of the few components in the set have a definite purpose, even the most despised phone condenser improving the results. The receiver works better with a cats whisker type of detector than a permanent type. In some cases and indoor aerial is giving satisfaction, but this type is not always satisfactory for reception of all four local stations.

(Letter from a Sunday Mail Reader July 17th 1932)
The merit of this receiver will be more readily appreciated after reading the letter from J E of Ashgrove:

I have successfully constructed your Mystery Crystal Set. As you already know, I have tried out a good few these last seven years. I used, on account of having a lot in hand, No 23 D.S.C wire for the 50 turn coil and 24 D.S.C for the 25 turn coil, using a .0015 mfd condenser between phones, having 120ft overall aerial. I met with amazing results. I bought in 4BG with wonderful punch. It was audible on the speaker (scientific type) two rooms away, on stud B, but when I switched on to stud A 4QG's volume decreased a bit, but I pulled in 4BK,4BC,4BH, and K4LW on the speaker. It was so strong that they could be heard 30ft from set.

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Very Selective and Sensitive

(by Proton.)
The Sunday Mail - Brisbane Australia April 16th 1933

Those readers who study our ratio-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.

Here are the components that you will acquire to construct the set. One bakelite panel 9 by 7 inches ; one wooden baseboard 9 to 7 by 1/2 inch; one .0003 m.f.d. variable condenser; one 3" plain dial; one glass enclosed crystal detector; one .001 m.f.d fixed condenser; one 3 1/2" inch length of 3" diameter tubing; one 1/4lb reel of 24 gauge D.S.C wire; one piece of empire cloth, 10 by 1 inches wide; four N.P. terminals, solder, and a coil of hook-up wire.

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 too 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. The punch two holes in the former at the spot, where the 25th turn of the 30 gauge wure ends, and thread the 30 gauge trough these to make it secure. No 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

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Now that you have completed the coil commence to mount the other component. The .0003 mfd 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 mfd turning condenser, and the .001mfd fixed phone condenser is mounted across the output terminals.

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.

If you have any questions regarding the Mystery Crystal Set Email me at, I hope you enjoy this article, I enjoyed making the Mystery crystal set and it came 3rd out of 19 crystal sets for performance, a lot of thought went into the construction to make it as close to a 1932 set as possible, I must have done a good job as it won the best reproduction section. Ray Creighton Brisbane Australia

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Updated 10th Aug 2000