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Old 24th Mar 2014, 4:05 pm   #21
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Default Re: Self built MW set with circuit diagram

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The cynic in me wonders about the true wisdom of building simple medium-wave radios
The optimist in me says what about the wonder of a simple crystal set giving sound? Just about the same way up from no radio in the 20's as the way 'down' from easy MP3/digital systems now.
 
Old 24th Mar 2014, 5:40 pm   #22
Variometer
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Default Re: Self built MW set with circuit diagram

I really find valves far more fun. You need ears like a bat to even hear a crystal set!
I recently wrote a document on how to make your own one valve receiver using either an HL2 triode or an EF91 pentode. Here is the synopsis:

Vintage Radio & Electronics
For The Home Constructor
by
Robert A. Wilson F.R.S.A.
A One Valve Battery Receiver

This e-book shows how to build a one-valve radio receiver using only a few components. It is perfectly safe for all ages, as the power supply is obtained from small 9 Volt batteries connected to make up the required 54 Volts for the high tension supply.
Two versions of the circuit are described. The first one, uses a very old HL2 triode valve. As this type is becoming more rare, a simple modification is described to make use of the far more common EF91 pentode valve instead of the HL2. EF91 valves are still in good supply, and not very expensive.
Some practical skills are required, such as the capability of using a few hand tools, including the use of a soldering iron.
Sources for all the components and materials are given in the book.
This e-book has been prepared with large text and images so that it is perfectly readable in e-readers that can handle PDF documents. That includes Kindles and Nooks. It can also be displayed on a computer, and printed out if so desired. 58 pages, 6,426 words and 64 images.


This e-book was a complete and utter failure and has now been abandoned (by me) However, I will be happy to e-mail it to anyone free of charge if they send me their e-mail address in a PM.

Or, and I don't know if this can be done, I could send the whole lot for inclusion in the forum somewhere. It is a PDF document that can be read with Acrobat Reader and can be read in computers, Kindles, Nooks etc The file is 2.2mb, so not too big and goes OK via e-mail.

I have offered it before on here, but not much response, although the latest recipient was absolutely delighted with it!

Bob
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Old 24th Mar 2014, 5:49 pm   #23
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Default Re: Self built MW set with circuit diagram

The big problem with valve designs for young beginners is the power requirement. This means building a mains supply, often more difficult and expensive (and dangerous) than the radio it powers, or messing about with lots of PP3s and D cells.
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Old 24th Mar 2014, 6:57 pm   #24
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Default Re: Self built MW set with circuit diagram

It doesn't take much "messing about" Attached is my HT battery. As for the LT, for the HL2 version, it is two 1.5 cells in series with a dropping resistor to get rid of the extra volt. For the EF91 version, it is a rechargeable 6 Volt battery. But I agree, with you, it probably does involve too much messing about - hence the failure of the e-book. Just an idea - probably a bad one!
Bob
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Old 24th Mar 2014, 7:58 pm   #25
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Default Re: Self built MW set with circuit diagram

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You need ears like a bat to even hear a crystal set!
With 'proper' headphones and the huge output of modern transmitters it isn't that quiet, and kids have much better hearing than I (54 years old) have.
 
Old 24th Mar 2014, 8:28 pm   #26
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Default Re: Self built MW set with circuit diagram

It depends where you live. People living near Droitwich used to report audible sound coming out of their gas cookers in the 30s. Presumably better earthing sorted out most of these problems, but I've heard stories of people living near to transmitters using the rectified signal to charge batteries. Bob in Preston might be a fair way from a strong signal (presumably Moorside Edge is his best bet).

A crystal set using the gas pipe as an aerial pulls in R5 from Droitwich here in Oxford. That's using a crystal earpiece, which I suspect is more sensitive than traditional dynamic headphones. A proper longwire aerial would almost certainly have brought in more stations, though they might all have come in at once.
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Old 24th Mar 2014, 8:42 pm   #27
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Default Re: Self built MW set with circuit diagram

I am 70 now and do have ears like a bat but afraid I have never been a great fan of the crystal set. I got a one valver to work at the age of 11 after failing with numerous cat's whiskers!
Bob
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Old 20th May 2014, 10:40 am   #28
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Default Re: Self built MW set with circuit diagram

There is nothing more off-putting than the reward for your hard work & concentration during the assembly process to be a deafening silence.
I haven't wide experience with crystal sets. I tried the various stages of the 'Ladybird' radio.
As a crystal set, with or without amplification it is unselective. The final stage is better, but the design uses obsolete components. The regen is determined by adjusting a 'postage stamp' trimmer, for which I used a cut down plastic knitting needle.
Whatever the design it ought to employ common & easy to obtain parts AND be a 'bullet proof' design.

In recent years I have made valve radios, the first being a TRF.
The important thing for the builder, no matter what they make is the 'rush' that comes when it actually produces sound. Because 'it' started off as a pile of bits and by their hands now does something wonderful.
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Old 20th May 2014, 11:18 am   #29
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Default Re: Self built MW set with circuit diagram

I have recently made a couple of crystal sets and am hooked. My girlfriend tells me I am half deaf, but i find two local stations, Sabras and the BBC Asian network, surprisingly loud. I am not much into Bollywood, but love Indian classical music. Anyway, the challenge for me is that you are working with the minimum, and it gives me a kind of datum for everything else. It's also magical - I had a German station coming in, soft but clear, fading in and out. I now want to make it more selective - two circuit tuning. Experimenting with basic components, coils, detectors, 'phones, caps, and hand building some, is very instructive!
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Old 20th May 2014, 3:18 pm   #30
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Default Re: Self built MW set with circuit diagram

Greenstar you are approaching a slippery slope. When I heard French and Spanish stations on a home built crystal set I was also hooked. There is a group in the USA who take this very seriously. You should find them easily on Google. There are lots of tips to improve performance that fascinated me.
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Old 20th May 2014, 5:14 pm   #31
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Default Re: Self built MW set with circuit diagram

Hi Tony, plenty of sites with all sorts of circuit suggestions on the web. A good one is to use the TL431 chip from a switchmode PSU as an audio amp that can be powered from 3volts.

Happy experimenting.

Ed
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Old 20th May 2014, 5:31 pm   #32
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Default Re: Self built MW set with circuit diagram

Thanks Ed. I have also wondered if the power from a strong station could power an amplifier - would of course need a separate tuned circuit. I would also like to make a small solar powered supply for my battery sets. 6-12v and vibrator/inverter. This interest creates a terrible dilemma! I love building things, but whenever I go to get parts I come home with another set. Need to be strong on my time management.
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Old 20th May 2014, 7:49 pm   #33
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Default Re: Self built MW set with circuit diagram

Hi Tony, plenty of modern Boost convertor chips available for low current use.
There was a recent design in Elektor called a "Joule Thief", designed to extract the last of the energy from normal cells to power LED's that would assist plant growth!

Ed
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Old 21st May 2014, 2:24 am   #34
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Default Re: Self built MW set with circuit diagram

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Originally Posted by G6Tanuki View Post
The cynic in me wonders about the true wisdom of building simple medium-wave radios for kids these days: you have to ask yourself if they will be at all impressed by something that only gives crackly earpiece-grade reception of a phone-in on BBC Radio Borsetshire where the elderly complain about the price of a fish-supper or the postmen dropping rubber-bands in the street.

There are, it has to be said, many more "entertaining" electronic constructions that can be done - and with a higher probability of success - using the various kits available from places like Maplin.
Absolutely! Even back in ~1962 I remember building my mandatory crystal set and being totally underwhelmed - and that was when MW had what we now refer to as "content". Older geezers may still find a thrill in the workings of a crystal set, but to an 8-10 year old, it's probably about as wonderful as a pair of tin cans connected via a piece of string. I'm delighted that my letters about fish-suppers and rubber bands are being networked on to BBC Radio Borsetshire.
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Old 21st May 2014, 12:19 pm   #35
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Default Re: Self built MW set with circuit diagram

I wonder how many children would have a conversation across the garden using mobile phones and then say "Wow we can do the same with a couple of tin cans and a length of string".
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Old 21st May 2014, 12:28 pm   #36
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Default Re: Self built MW set with circuit diagram

I think it depends on what kind of kid you are. From about the age of six to twelve, when I actually made one, I was obsessed with horn gramophones. When I first saw one - a toy thing of red plastic, that played 45's without batteries, I think, I was totally amazed that something would work without electricity. I then understood, slowly, that there were technologies that had been abandoned which worked very effectively and elegantly.
Low tec has it's appeal. Thus I don't think we should ever abandon MW broadcasting - a simple, bullet proof technology with international range.
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Old 21st May 2014, 1:45 pm   #37
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Default Re: Self built MW set with circuit diagram

We seem to be losing the plot here, the thread is about MW radio kits, or the problems with building same.
Does anyone have any relevant input to round it off?
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Old 21st May 2014, 2:33 pm   #38
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Default Re: Self built MW set with circuit diagram

Crystal sets depend on where you live.

Mine were successful and loud enough to hear the headphones across a room. But living a handful of miles away from Moorside Edge 'Northern Regional' transmitter made the difference.

The problem later was making things that did not pick it up!

I fear that medium wave broadcasting is on the way out. It all comes down to money. Even if the transmitters aren't being run, it costs a lot just to keep the masts maintained in a safe condition, and high sites are in demand from the wind farm firms.

I could imagine a charitable preservation trust maintaining a medium wave transmitter and running it up occasionally rather like one of those steam museums, but the cost of keeping the masts in a safe condition regarding visitors and neighbours may be the problem.

Using a far smaller antenna structure with much reduced range might be feasible, otherwise it's just pantry transmitters.

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Old 21st May 2014, 5:23 pm   #39
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Default Re: Self built MW set with circuit diagram

Quasar have quite a good range of radio kits, MW, SW and FM!
http://www.quasarelectronics.co.uk/C...ctronic-radios
I've bought some more industrial stuff from them and that was good.

B
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Old 22nd May 2014, 9:19 pm   #40
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Default Re: Self built MW set with circuit diagram

I remember building on stripboard lots of different MW radio designs mostly based on the ZN414. They were always disappointing because the lack of selectivity meant BBC Radio Bristol was audible over most of the band and it was difficult to receive any more than two or three stations.
The most successful radio I built was a FM kit based on the TDA7000. It worked very well indeed. It was easy to build with only a couple of small coils to wind and nothing to align. I probably built it when I was about 12 or 13 and it was very satisfying when it worked.
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