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Old 12th Jan 2019, 8:09 pm   #1
ionburn
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Default "The Works" Crystal Radio

Perhaps a bit of a review of something most would not think about here, but may be helpful to anyone buying this as a present for a younger relative.

I recently saw elsewhere this radio mentioned, so I thought as a pleasant diversion I would obtain one of these and see how it went (as they are reasonably cheap - 5 at the moment).

My first thoughts on opening the box was that the product was generally a bit cheaply made (expected really). On looking at the instructions I found that for one thing there was no schematic, and the instructions really required some skill or expert knowledge. Perhaps more serious is that the (supposed) Germanium crystal diode was marked ST4148 (err....).

I proceeded to construct, finding it tricky at times, but the real point of problem was that the brass tuning slider did not readily contact the coil throughout the range. This required careful adjustment (bending of slider rod).

I did finally get things working, with my loft long wire aerial and plumbing system earth (three stations, one of which loud enough for reasonable listening - I should point out that I did not spend a lot of time with the many possible variables). The original diode gave no response except for some noise (high imedance so some kind of picked up noise?). My working system used a Russian D311 diode (Genuine Germanium and seems a useful diode for crystal sets). I plotted a curve for the ST4148 - Silicon as suspected.

Looking online I notice this set (or very similar design) is sold elsewhere, and another builder (I think in the States) showed me part of a different manual showing a schematic, which was identical to the one I drew from the circuit.

Like most things these days it appears to originate from China.

All in all, an interesting deviation from serious stuff, but I think that many children who received for Christmas this will be dissapointed. I have been tinkering with crystal sets, and found my 85mm 50 turn multitapped coil (24SWG) with tuning capacitor (the kit uses self capacitance of coil rather than additional capacitor) with D311 diode and using the same aerial / earth setup gave far superior performance. It does seem useful for a minimally working setup for reference though.

https://www.theworks.co.uk/p/educati.../5015934323670
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Old 12th Jan 2019, 8:17 pm   #2
G6Tanuki
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Default Re: "The Works" Crystal Radio

Apart from the novelty-value, is there anything still providing crystal-set-usable signal levels on medium-wave that kids would be interested in listening to?

The local [Swindon] Absolute-Radio transmitter went off-air last spring; the only other MW stations I'd expect to get here on a crystal-set are 5-Live and Smooth Radio. Hardly compelling listening!
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Old 12th Jan 2019, 8:31 pm   #3
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Default Re: "The Works" Crystal Radio

The strongest signal I received was Absolute Radio (not checked which transmitter it may be as yet). On the homemade coil setup I mentioned, with a good quality headset it was excellent. On the kit it was listenable. Here in Lincolnshire I think my goal would be Caroline as, during the daytime, reception is good with normal radio, but, for kids, it would probably be a step too far. No, a crystal set is not something which would give the instant results it once did. More for the expert now.
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Old 12th Jan 2019, 8:47 pm   #4
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Default Re: "The Works" Crystal Radio

Quote:
Originally Posted by G6Tanuki View Post
Apart from the novelty-value, is there anything still providing crystal-set-usable signal levels on medium-wave that kids would be interested in listening to?

The local [Swindon] Absolute-Radio transmitter went off-air last spring; the only other MW stations I'd expect to get here on a crystal-set are 5-Live and Smooth Radio. Hardly compelling listening!

I think the mere act of getting *something* out of the thing is what this is all about. I can't seriously believe anyone would want to use it for practical listening these days. It's a shame this wasn't better implemented though, especially putting in a silicon diode instead of germanium. The average child (or child's father) is very unlikely to suss that one out and will assume the kit should work "as is". It will almost certainly consign the thing to landfill, unfulfilled
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Old 12th Jan 2019, 11:12 pm   #5
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Default Re: "The Works" Crystal Radio

As long as 15 years ago I tried, with all my past radio experience at my disposal, to get a 'toy' crystal set - 'John Adams' in that case, with a fixed tuning coil and variable capacitor and germanium diode and crystal earpiece - to work with a very long wire and a good earth, and still failed. That was in East Sussex.

The only thing I didn't try was a bias battery to nudge the diode up to the 'almost on' point, as I felt that the whole point of a crystal set was that it should miraculously work without any integral power.

Back in my teens I had no difficulty getting home made crystal sets working here on urban Tyneside, the main difficulty being that the set tended to receive more than one station at a time.
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Old 13th Jan 2019, 2:58 pm   #6
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Default Re: "The Works" Crystal Radio

Quote:
Originally Posted by evingar View Post
I think the mere act of getting *something* out of the thing is what this is all about. I can't seriously believe anyone would want to use it for practical listening these days. It's a shame this wasn't better implemented though, especially putting in a silicon diode instead of germanium. The average child (or child's father) is very unlikely to suss that one out and will assume the kit should work "as is". It will almost certainly consign the thing to landfill, unfulfilled
I would agree with that. I think, for practical purposes, a crystal set for a child's project is a thing of the past. I would re-iterate though that the Absolute radio station I received with my homemade setup was good for general listening so a well thought out setup will still work. As I have no shortage of components I am not inclined to pursue their 'incorrect' diode. I have, though. posted the fact as a review on their website. Really it is an issue under trade's descriptions as they do state Germanium diode in the manual so any buyer with a problem should be able to get it sorted.
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Old 13th Jan 2019, 3:18 pm   #7
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Default Re: "The Works" Crystal Radio

The big problem with crystal sets for children is that their performance will be highly dependent on the presence of strong local signals. If you live in Birmingham then it will be easy to get impressive results as Droitwich is just down the road, but if you live in Norwich or Aberystwyth you will struggle to hear anything at all.

I agree about the unacceptability of a silicon diode in this kit. The cost saving over Ge will be tiny, so I wonder if this was just a supply oversight by someone who didn't understand the implications.
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Old 13th Jan 2019, 4:12 pm   #8
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Default Re: "The Works" Crystal Radio

I bought said kit today (the branch of 'The Works' in the 'Glades' shopping centre, Bromley if it matters). I've not attempted to build it yet but I did check the diode. My multimeter gives a forward voltage drop of 0.7V for it, so I am pretty sure it's silicon. So it wasn't a one-off mistake in the 'ionburn's kit.

What's the betting that the ST4148 is a 1N4148?

A schottky diode might work in place of a germanium one, but I doubt you'd get a strong enough signal to use the normal silicon diode.
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Old 13th Jan 2019, 5:09 pm   #9
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Default Re: "The Works" Crystal Radio

I see it uses a crystal earpiece, I wonder if there is a resistor across it, 20 to 100k does make a noticeable improvement in sound level. This stops the earpiece merrily charging up solely relying upon the leakage of the diode and earpiece to discharge. There is a "Works" in Maidenhead, I might get one.

The silicon junction diode cockup is probably because of a "buyer" being in charge. Has anyone told "Works"? I will if I get a silicon junction diode.
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Old 13th Jan 2019, 5:18 pm   #10
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Default Re: "The Works" Crystal Radio

No, there's no resistor in parallel with the earpiece. And no capacitor in the tuned circuit. I guess it relies on the stray capacitance between the aerial and earth.

The only components are the adjustable tuning coil (which you wind yourseld on a cardboard tube then sand off the enamel to provide a contact point for the adjustable tap thing), a diode, and the crystal earphone.
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Old 13th Jan 2019, 5:32 pm   #11
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Default Re: "The Works" Crystal Radio

There are two reviews on the web site, both not happy and with one star. One of the reviews noted the silicon diode, was that you ionburn?
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Old 13th Jan 2019, 5:38 pm   #12
TonyDuell
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Default Re: "The Works" Crystal Radio

Incidentally, the so-called instructions claim the diode contains a germanium crystal. I suspect that was originally specified and then some buyer or whatever thought 'a diode is a diode, the 1N4148 is the cheapest'.
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Old 13th Jan 2019, 5:45 pm   #13
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Default Re: "The Works" Crystal Radio

Quote:
Originally Posted by Nuvistor View Post
There are two reviews on the web site, both not happy and with one star. One of the reviews noted the silicon diode, was that you ionburn?
That was me. I did write a further review after I had built it, but that does not seem to have been accepted. The other review is someone else.
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Old 13th Jan 2019, 5:53 pm   #14
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Default Re: "The Works" Crystal Radio

I have built crystal sets to this design in the past (crystal earpiece without a resistor) and they do work acceptably well with a long aerial and a good signal, though that's not to say a resistor wouldn't have improved things.
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Old 13th Jan 2019, 6:43 pm   #15
Ian - G4JQT
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Default Re: "The Works" Crystal Radio

An interesting though depressing thread.

My father recognised my interest in things electrical and bought me a crystal set from the ads at the back of Wireless World, yes, WW, not PW! OK, this was 1970 in Bury Lancs with plenty of MW stations.

It had a plastic base board, coil-spring contacts with a ferrite rod, varicon capacitor. germanium diode and crystal earpiece. Used my curtain rail as the antenna and radiator pipe as the earth. It worked; lit the 'fuse' which is why I'm here 50 years later.

It's very disappointing that poor kits, aimed particularly at youngsters, are still being sold. Maybe even if it worked, MW has changed so much that little if anything would be audible. But poor kits like this and the Chinese radio kits discussed elsewhere on the forum ensure that the fuse of the recipients is unlikely to be lit, and that's very sad...

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Old 13th Jan 2019, 7:55 pm   #16
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Default Re: "The Works" Crystal Radio

I made a crystal set when but a young'un with a bit of galena from a geology display pack bought in Wales, it worked well.
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Old 14th Jan 2019, 6:16 am   #17
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Default Re: "The Works" Crystal Radio

My first crystal set was the first bit of the Ladybird book 'Making a Transistor Radio'. It worked first time. I went on to complete the 3-transistor set in that book and I still have it.

I agree about poor quality instructions being a big 'turn off' for those starting out. You need a little success early on or you wonder if there's any point in (say) radio/electronics construction. But this is not a new problem. Over Christmas I built a (off-topic, not electronic) kit from the early 1970s. A Meccano Clock Kit 2 (makes a striking pendulum clock). I got it working after a lot of adjustment to the strike countwheel. But I feel that the only reason I managed it is that I know how such clocks should work and knew what to adjust, etc. Somebody starting out wouldn't have a hope of getting it running.

Same with the crystal set. Many of us here know how to check if a diode is germanium or silicon, have the equipment to do so and know why the former is needed for a crystal set. Many of us could check if a signal is being tuned in (even if the detector diode and earpiece are unsuitable or faulty). But somebody starting out, with no test gear, no knowlege of radio? Not a chance.
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Old 14th Jan 2019, 6:46 am   #18
G4YVM David
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Default Re: "The Works" Crystal Radio

George Dobbs book...excellent. I still have mine and managed to get him to sign it a few years back.
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Old 14th Jan 2019, 3:00 pm   #19
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Default Re: "The Works" Crystal Radio

Like those above the first thing I built was a crystal set using what I think was an OA90. My Dad brought home part of a PW containing an article on building one. We never had the whole magazine. I guess it was in the late 50's. I also saved up and bought a red spot transistor so it had a one transistor amp. This morning I bought one of the Works kits. Have only read the instructions/info so far. Did not seem to bad. Did notice the bit on the "crystal" being germanium which I think make the addition of a silicon diode worse as when it does not work most inexperienced people would assume the diode was of the correct type and perhaps not consider it to be the reason it did not work. I will build it when I have time.

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Old 14th Jan 2019, 4:01 pm   #20
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Default Re: "The Works" Crystal Radio

Well if nothing else this thread as sold a few more of the kits.
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