Crystal Radio Sets

Jim Martin

Does any one remember these little crystal radio sets which used to be advertised in newspapers and comics in the 1950's?

http://www.radiomuseum.org/r/ivory_ivalek.html

I always wanted one but it never happened, maybe I'll pick up a second-hand one.

It still fascinates me that radio signals can be picked up without the need for a power supply!

watty

I've built many "Crystal" sets in late 60s and early 70s. All actual Germanium or Silicon diodes and a very high impedance ceramic (AKA Crystal) earphone.

They don't have enough signal to drive modern earbuds usually.

You can make one from parts of a 2 Euro pound shop radio. Maplin also has parts.

You need a ferrite rod with 200 to 500 turns of fine enamel wire.
A variable capacitor about 20pF to 500pF (tie the two sections of a pocket radio 2 gang "polycon" together)
Germanium Diode type OA47 or similar (a Silicon 1N4148 needs more power, a schottky BAT34 something in between).

1nF (=1000pF or 0.001uF) capacitor
22k to 100k resistor, or resistance of hi-impedance 2K or 4K headphones
Ceramic earpiece.

a good earth

a metal cored clothes line as aerial

Typical circuit
http://www.uoguelph.ca/~antoon/circ/whisker1.html
You can leave off the coil taps

Good photo here showing the type of earphone.
http://sci-toys.com/scitoys/scitoys/radio/ten_minute_radio.html

You MUST use that type of crystal/ceramic earpiece. It doesn't work with a regular earphone.

After dark reception is better,


The "crystal" referred originally to an actual piece of crystal (galena possibly) with a sharp nickle wire creating the semiconductor junction rectifier (diode). The wire is the "cat's whisker". It would have to be carefully tweaked to get reliable reception. A modern diode or rectifier has the junction in the body of the semiconductor and the wire connections are just connections.

Jim Martin

Thanks 'Watty' - I built one myself with instructions from a little book I bought in the Science Museum but I could only pick up one station, BBC Radio 2, when I was living in Bedfordshire at the time, I don't know what I did wrong but it was probably an aerial/earth problem!

stylers

the problem of only picking up one station is most likely due to being right next to a MW transmitter, and the fact that crystal sets have little or no selectivity - when I used to build crystal sets as a very young chap, I had the same problem, which was due to being a stones throw from the ballycommon transmitter near tullamore.. but now that its gone, that might not be a problem any more (or depending on one's fondness for national MW services).

As watty suggests, those el cheapo 2-euro shop radio's probably contain all the bits you need apart from the headphones - the ferrite rod (probably a flat thin bar type), a germanium diode (the crystal) and the capacitor.

If you wanted to build something with much better selectivity and results, you can always try a regenerative receiver. ok, so its a small bit more complicated, and requires power, but it will drive normal headphones and the results can be excellent..

watty

The fewer turns to couple aerial and earth and the higher the earphone impedance the sharper the tuning is.

On Car radios in 1970s you could ONLY get one station on whole MW near Lisburn due to Lisnagarvey. At one time Home Service and then R.Ulster

For MW/LW I've built TRF radio in match box with AAA battery. No separate detector. One or other of the 5 really low power Audio amp transistors acts as detector. Battery lasts over 6 months. 32 Ohm earphones.

For VHF I built super-regen in a matchbox, the tuning coil had plastic drinking straw. At one end is piece of brass bolt and the other a small ferrite slug. So would tune 70MHz to 140Mhz or more and pickup all the FM radio, Mobile and Air. AM or FM.
Again a AAA battery, about 1 months use.

I gan put schematics on my web site and sketch of assembly if anyone interested.

recycler1

watty wrote: »

I've built many "Crystal" sets in late 60s and early 70s. All actual Germanium or Silicon diodes and a very high impedance ceramic (AKA Crystal) earphone.

They don't have enough signal to drive modern earbuds usually.

You can make one from parts of a 2 Euro pound shop radio. Maplin also has parts.

You need a ferrite rod with 200 to 500 turns of fine enamel wire.
A variable capacitor about 20pF to 500pF (tie the two sections of a pocket radio 2 gang "polycon" together)
Germanium Diode type OA47 or similar (a Silicon 1N4148 needs more power, a schottky BAT34 something in between).

1nF (=1000pF or 0.001uF) capacitor
22k to 100k resistor, or resistance of hi-impedance 2K or 4K headphones
Ceramic earpiece.

a good earth

a metal cored clothes line as aerial

Typical circuit
http://www.uoguelph.ca/~antoon/circ/whisker1.html
You can leave off the coil taps

Good photo here showing the type of earphone.
http://sci-toys.com/scitoys/scitoys/radio/ten_minute_radio.html

You MUST use that type of crystal/ceramic earpiece. It doesn't work with a regular earphone.

After dark reception is better,


The "crystal" referred originally to an actual piece of crystal (galena possibly) with a sharp nickle wire creating the semiconductor junction rectifier (diode). The wire is the "cat's whisker". It would have to be carefully tweaked to get reliable reception. A modern diode or rectifier has the junction in the body of the semiconductor and the wire connections are just connections.

I did exactly the same, and in the late 60's, early 70's, too. I next went on to a one valve, battery powered, "Hear All Continents" receiver - with plug in Denco coils. This was advertised in the radio club section of "Our Boys" magazine. (Was it Our Boys?)
I then wanted a FRG7 shortwave set, but had to settle for a home built, dual superhet from a 1975 Practical Wireless design. Happy days.

I finally got that Frog, last year, from EBay! It's in mint condition but really needs a good external aerial(s). I have the space, but no longer the interest, to set up an aerial farm. If you know anyone who'd give it a good home I'd be happy to pass it on, f.o.c.

recycler1

watty wrote: »

For VHF I built super-regen in a matchbox, the tuning coil had plastic drinking straw. At one end is piece of brass bolt and the other a small ferrite slug. So would tune 70MHz to 140Mhz or more and pickup all the FM radio, Mobile and Air. AM or FM.
Again a AAA battery, about 1 months use.

I gan put schematics on my web site and sketch of assembly if anyone interested.

Go on then, this is a real trip down memory lane. (If I remember rightly, the super-regens were the ones that hissed away until the signal was tuned in.)

watty

Ok. It may take a day or two to find.

watty

I can't find them. It was 19 years ago!

I did find the actual radio. Anyway have a look at my shack in the shack thread.

Home made battery holder for an AAA size cell.

Coil is tuned with a small straw with ferrite at one end (lowers frequency) and piece of brass (raises frequency) at the other by pulling it in/out. About 60MHz to 140MHz, in collector of transistor. The twisted enamel wire is a feedback capacitor to make it oscillate. The larger ferrite slug is in the emitter and has audio take off and aerial in.


The yellow wires for a miniature speaker or earpiece.
The single red wire is possibly aerial.
Four transistor amplifier. Low gain stages reduces battery current.

It all fits in a small matchbox.

recycler1

watty wrote: »

I can't find them. It was 19 years ago!

I did find the actual radio. Anyway have a look at my shack in the shack thread.

Home made battery holder for an AAA size cell.

Coil is tuned with a small straw with ferrite at one end (lowers frequency) and piece of brass (raises frequency) at the other by pulling it in/out. About 60MHz to 140MHz, in collector of transistor. The twisted enamel wire is a feedback capacitor to make it oscillate. The larger ferrite slug is in the emitter and has audio take off and aerial in.


The yellow wires for a miniature speaker or earpiece.
The single red wire is possibly aerial.
Four transistor amplifier. Low gain stages reduces battery current.

It all fits in a small matchbox.

Yeah, brings back memories, all right.
Many's the bit of veroboard I used.
(I was never that comfortable etching PCB's - just too many holes to drill.)

That's one impressive shack!

stylers

good stuff watty, you also like cramming as many components as possible onto vero you didn't cut too many tracks either lol

chalkitdown

recycler1 wrote: »

I did exactly the same, and in the late 60's, early 70's, too. I next went on to a one valve, battery powered, "Hear All Continents" receiver - with plug in Denco coils. This was advertised in the radio club section of "Our Boys" magazine. (Was it Our Boys?)
I then wanted a FRG7 shortwave set, but had to settle for a home built, dual superhet from a 1975 Practical Wireless design. Happy days.

I finally got that Frog, last year, from EBay! It's in mint condition but really needs a good external aerial(s). I have the space, but no longer the interest, to set up an aerial farm. If you know anyone who'd give it a good home I'd be happy to pass it on, f.o.c.

Hi, I would be very happy to take your 'frog' from you, I have always wanted one. I would be more than happy to pay for any shipping. Will have to dig out my old ATU as I can only fit a long wire from here though.

watty

PM only. NO on thread trading.

recycler1

watty wrote: »

PM only. NO on thread trading.

PM Sent.

chalkitdown

PM recieved, many thanks Recycler, will have a lot of craic with this, very generous of you.

watty

Adding 22m of wire and an Aerial Match unit, plus a couple of ESB earth spikes makes a big difference for Frogs.

chalkitdown

watty wrote: »

Adding 22m of wire and an Aerial Match unit, plus a couple of ESB earth spikes makes a big difference for Frogs.

22M! GF would have a heart attack! lol.
Do you think I could use a helically wound section to shorten it?

watty

A big enough loading coil and you can even match a 2m whip at 1.8MHz.

chalkitdown

How many turns on a bog roll would I need to shorten it by half? And would I be better having it at any particular point on the long wire?

Numeric

it works like Radio set in Apocalypse world here http://tellmeday.com/en/articles/view/10/ ?

matdawgi

recycler1 wrote: »

Yeah, brings back memories, all right.
Many's the bit of veroboard I used.
(I was never that comfortable etching PCB's - just too many holes to drill.)

That's one impressive shack!

Can you email me the schematic or tell me where it is posted...for the 70-140 mhz crystal set that you have posted in the photo...the breadboard...thanks...matt...

watty

I don't have the exact schematic any more I built it nearly 20 years ago.


Receiver transistor is top left.
It's a 1 transistor "super-regenerative" receiver with a 5 transistor audio amplifier. Not a "crystal set".

This is similar but needs more audio amp
http://www.vk2zay.net/article/195

On my circuit the audio is taken from "pot" end of lower coil which is a fixed resistor. I have a fixed tuning capacitor (just the stray capacitance) and the collector coil is tuned via a straw with ferrite slug at one end (lowers frequency) and cut off piece of brass bolt (raises frequency) with coil length gap between them. It runs of AAA cell (1V to 1.57V alkaline).

Here is another similar one with an IC audio amp.
http://www.jbgizmo.com/page23.html#plans

Often 433MHz wireless remote extenders, wireless door bells or Wireless weather stations use a similar one transistor receiver for ASK/OOK data. You will find one inside Heaton's €8 wireless doorbell chime unit.

jmcc

Great links Watty,
I'd forgotten how downright addictive RF engineering can be.

Regards...jmcc

humaxf1

I hope these circuits are "type approved"

:P

Taildragon

For a real "blast from the past", look out for the Ladybird book "Making a transistor radio"

http://www.theweeweb.co.uk/ladybird/ladybird_book_detail.php?id=2950

http://www.flickr.com/photos/paopix/4826215753/in/photostream/

Finding the specified components wouldn't be easy these days, but the basic crystal set design illustrated would still be achievable with modern substitutes.

watty

They are receivers. Receivers for personal use don't need type approval.

Though you do have to be careful with power levels of Direct Conversion receivers. A screen can and tuned rf buffer amp with good reverse isolation is sensible before you go making one connected to a good outdoor aerial.

watty

Maplin sells those high impedance "crystal earphones" (actually ceramic). Regular headphones are not sensitive enough.

http://www.flickr.com/photos/paopix/4826215753/in/photostream/

An OA47 will work as diode. They are still readilly available.

The "polycon" tuning capacitors used in pocket radios are easy to get. About 270 pf per section, so parallel the sections works better.

larger ferrite rods are hard to find. Smaller ones are easy to get.

The illustrated radio in the link has no transistors, it's just the "classic" crystal set using a germanium diode instead of galena crystal and cat's whisker.


The three transistor radio
http://www.flickr.com/photos/paopix/4826228351/in/photostream/
can use 2 x 1n4148 reversed, and 3 x BC107/BC147/BC547/2N3904 and reverse the battery, but only use 3V (2 x AA cells)

Connect the 390k and 2 x 150k to the collectors instead of supplies
Omit the 33k from base to ground on 2nd transistor
insert a 2nd 10uF capacitor 3rd transistor base to 10 K volume control "+" to base
Reverse the polarity of the existing three electrolytics 10uF, 100uF and 10uF

Taildragon

I came across this website:

http://www.crystal-radio.eu/index.html

More than you ever knew you wanted to know about crystal radio design & constructions. Interesting section on diode types and biasing effects.

http://www.crystal-radio.eu/endiodes.htm

Mike 1972

watty wrote: »

You need a ferrite rod with 200 to 500 turns of fine enamel wire.

Given that in many parts of Ireland the only strong broadcast (AM) signal these days is 252 KHz longwave I daresay one would need to be closer to 500 than 200 (more turns = lower frequency)

watty

I can get UK AM in Limerick on Car Radio, in Daytime.

But only if I turn the engine off.

Night time plenty of AM.

Mike 1972

watty wrote: »

I can get UK AM in Limerick on Car Radio, in Daytime.

Yes but your car radio probably has more gain than a crystal set.

Now if youd told me you could get them on a supermarket portable................:D