Radio Shack made a crystal radio kit back in the 70's and 80's. Germanium diode, pre-wound coil with a ferrite core, variable cap and that oh so infamous ear piece. I was surprised at just how selective it was. I believe it went under the Archer brand name. Many nights I fell asleep with that ear piece in, listening to our local AM station.
the kit i had was different, it didnt have the tuning capacitor, had the diode and a coil but you had a metal slider than ran across the coil and you had to sand the varnish off where the rod contacted the coil. you would slide the rod across the coil to tune in different stations. spent many a night since this is when am was at its best listening to local radio thru a earpiece. dad stretched a wire from the garage to my bedroom window and it stayed there til the wire rusted thru and broke eventually. btw, thanks for the homage to steve1989mre, that was great and i see i have a new channel to relax to after a sucky day at work.
I made dozens of crystal radios BITD (early 70’s)… most didn’t work. Then, I just built my own design, worked first time. Germanium diode of choice back then (in UK) was the Mullard OA91 ! Transistors AC128 & AC129’s were favs too… also useful, you could scratch off the paint and use them as phototransistors 👍🏻
Haha, a few years ago I built a crystal radio with actual crystals. :) I got some galena crystals (also tried pyrite, didn't work too well, and also silicon carbide crystals, those worked). I potted each crystal in a low-melt alloy, I think Cerrolow, for good electrical contact on one side, and probed them with a whisker until I found a good spot. I used a 3d-printed jig to hold them in place in the position I found. It worked, but like yours not too great. On a side note, those silicon carbide crystals are also useful for another little fun physics experiment. SiC is a N-type semiconductor, with a band gap that allows you to build a home-made LED. In fact, the first LED in history was made of it. Not commercially used these days because it has very low quantum efficiency. But if you connect a battery's negative terminal to the crystal and probe its surface with a whisker connected to the positive, you will find spots on the crystal that glow orange-yellow. You need at least 3V for that since that is the threshold voltage for SiC. The light produced is fairly dull so better do it in a semi-dark room or you may not see it.
Built a Crystal Radio back in the 80s. It would have been part of my Tandy / Radio Shack 200-in-1 kit. I would love to build a real crystal radio with a cats whisker and Galena crystal.
Definitely a British-origin kit with the use of "aerial" and the list of frequencies is for BBC AM stations. Sadly several of these are now disappearing because of the rush to digital. I built a kit like that when I was a kid and it got me hooked. I wound the coil on a jam jar. I have recycled bits from it several times and the 365+365pF capacitor from the kit is in my QRP tuner now.
I had a kit a bit like this but with a sliding bead on the coil (made on a cardboard former) for tuning - back in the 80s. Dad helped me add a tuning capacitor and that made it much more selective. I had a long wire aerial outside and used to pick up all kinds of broadcast at night. I added a two transistor amplifier later on so it could play from a speaker. Brilliant way to learn basic electronics and the basics of RF and AM radio transmissions.
The Gillette blue blade, a length of graphite (pencil lead), a safety pin to mount the lead and that takes care of the 'cats whisker'. Worked like a charm 65 years ago. Don't know if blue blades are still available, but they were the go to in my day. The newer blades do not have the same crystalline structure.
I made one from a kit in the 80's. Winding the coil was a right pain, I think it had about 500 turns with taps every 50 turns, or something. It worked realy well though.
The reason for low selectivity is the low impedance of the headphone, as it becomes part of the LC thus diminishing the quality factor of the inductor. I used to use a 2 kOhm phones as a child and they would provide for much better selectivity.
2:46 I heard you can also make a diode out of an oxidized copper* penny. But I also heard that that is incredible finicky. *=(has to be copper, but most pennies today are alloys)
Those kind of tuning capacitors are more for VHF than MW AM, guess they used it to cut down on cost, a proper one needs to be around 500-700pF to cover the entire band.
The small variable capacitor was usually DOUBLE and used in transistor radios. One section for the LC input and one for the local oscillator. The tuning range with the coil easily covers the MW range.
The polyvaricon, or so they are called, (variable condenser (capacitor) made of polymer- PVC) are usually of 310-365pF, per each section (one for the antenna tuning and the other for the oscillator section) and they're for the MW and the SW bands. The metal dielectric air gang capacitors are usually found in the Vaccum Tube and some models of the solid state receivers; the capacitance might be around 350-500pF each section. Some capacitors would have a larger value for the antenna section (ie, tuning to some lower frequency) and a little smaller value for the oscillator section (the local oscillator in the superhet will have to oscillate 455KHz higher than the signal the antenna section is tuned to) De VU2RZA
Radio Shack made a crystal radio kit back in the 70's and 80's. Germanium diode, pre-wound coil with a ferrite core, variable cap and that oh so infamous ear piece. I was surprised at just how selective it was. I believe it went under the Archer brand name. Many nights I fell asleep with that ear piece in, listening to our local AM station.
I used to have the same one, a good antenna, a good ground and you were good to go, real great stuff.
Always enjoy when a channel pays homage to Steve1989MREInfo. 😂
the kit i had was different, it didnt have the tuning capacitor, had the diode and a coil but you had a metal slider than ran across the coil and you had to sand the varnish off where the rod contacted the coil. you would slide the rod across the coil to tune in different stations. spent many a night since this is when am was at its best listening to local radio thru a earpiece. dad stretched a wire from the garage to my bedroom window and it stayed there til the wire rusted thru and broke eventually. btw, thanks for the homage to steve1989mre, that was great and i see i have a new channel to relax to after a sucky day at work.
I made dozens of crystal radios BITD (early 70’s)… most didn’t work. Then, I just built my own design, worked first time.
Germanium diode of choice back then (in UK) was the Mullard OA91 !
Transistors AC128 & AC129’s were favs too… also useful, you could scratch off the paint and use them as phototransistors 👍🏻
Very nice coil winding!
Haha, a few years ago I built a crystal radio with actual crystals. :) I got some galena crystals (also tried pyrite, didn't work too well, and also silicon carbide crystals, those worked). I potted each crystal in a low-melt alloy, I think Cerrolow, for good electrical contact on one side, and probed them with a whisker until I found a good spot. I used a 3d-printed jig to hold them in place in the position I found. It worked, but like yours not too great.
On a side note, those silicon carbide crystals are also useful for another little fun physics experiment. SiC is a N-type semiconductor, with a band gap that allows you to build a home-made LED. In fact, the first LED in history was made of it. Not commercially used these days because it has very low quantum efficiency. But if you connect a battery's negative terminal to the crystal and probe its surface with a whisker connected to the positive, you will find spots on the crystal that glow orange-yellow. You need at least 3V for that since that is the threshold voltage for SiC. The light produced is fairly dull so better do it in a semi-dark room or you may not see it.
That's a wonderful piece of information on homebrew LED.
Thanks 👍
De VU2RZA
What do you do with the rest of the crystals? They are so hard... put them in your garden?
Built a Crystal Radio back in the 80s. It would have been part of my Tandy / Radio Shack 200-in-1 kit.
I would love to build a real crystal radio with a cats whisker and Galena crystal.
Definitely a British-origin kit with the use of "aerial" and the list of frequencies is for BBC AM stations. Sadly several of these are now disappearing because of the rush to digital. I built a kit like that when I was a kid and it got me hooked. I wound the coil on a jam jar. I have recycled bits from it several times and the 365+365pF capacitor from the kit is in my QRP tuner now.
I had a kit a bit like this but with a sliding bead on the coil (made on a cardboard former) for tuning - back in the 80s. Dad helped me add a tuning capacitor and that made it much more selective. I had a long wire aerial outside and used to pick up all kinds of broadcast at night. I added a two transistor amplifier later on so it could play from a speaker. Brilliant way to learn basic electronics and the basics of RF and AM radio transmissions.
The Gillette blue blade, a length of graphite (pencil lead), a safety pin to mount the lead and that takes care of the 'cats whisker'. Worked like a charm 65 years ago. Don't know if blue blades are still available, but they were the go to in my day. The newer blades do not have the same crystalline structure.
My grandpas crystal radio he build at his times,had galenit PbS detektor...and he search with a sharp rod tip the best or loudest spot on it....
I made one from a kit in the 80's. Winding the coil was a right pain, I think it had about 500 turns with taps every 50 turns, or something. It worked realy well though.
It reminds me of my 70's. The crystal radio had one germanium diode (detector) 1N60, a high-impedance crystal earpiece and other parts.
im surprised it worked with so little parts. Crazy!👍
Of course, Grandad can no longer hear the audio so that is why the radio must be listened to by a grandkid.
The reason for low selectivity is the low impedance of the headphone, as it becomes part of the LC thus diminishing the quality factor of the inductor. I used to use a 2 kOhm phones as a child and they would provide for much better selectivity.
The cats whisker touches galena
ha..ha..cute pic! that's me back in the day also!! I didn't have any instructors though...
The former used crystal is galena or galenite.
Yup, any crystal radio, that I built, would get swamped out by the local blowtorch.
2:46 I heard you can also make a diode out of an oxidized copper* penny. But I also heard that that is incredible finicky.
*=(has to be copper, but most pennies today are alloys)
Great photo!
Pretty sure I was already subscribed but.....
I’ll do it again.
I didn't think they would work any more, considering everything went digital :(
how is this possible!! I was thinking about your channel and this project. but i couldn't find it on the earphone, 73 from Turkey.
TA7TUR
Since a square wave is made of a lot of sine waves, how can we filter and separate those sine waves?
It might be very interesting to know how.
ruclips.net/video/h68iJ8JiHFQ/видео.html
Those kind of tuning capacitors are more for VHF than MW AM, guess they used it to cut down on cost, a proper one needs to be around 500-700pF to cover the entire band.
The small variable capacitor was usually DOUBLE and used in transistor radios.
One section for the LC input and one for the local oscillator.
The tuning range with the coil easily covers the MW range.
The polyvaricon, or so they are called, (variable condenser (capacitor) made of polymer- PVC) are usually of 310-365pF, per each section (one for the antenna tuning and the other for the oscillator section) and they're for the MW and the SW bands.
The metal dielectric air gang capacitors are usually found in the Vaccum Tube and some models of the solid state receivers; the capacitance might be around 350-500pF each section.
Some capacitors would have a larger value for the antenna section (ie, tuning to some lower frequency) and a little smaller value for the oscillator section (the local oscillator in the superhet will have to oscillate 455KHz higher than the signal the antenna section is tuned to)
De VU2RZA
@@subramanianr7206 Exactly!