DIY AM receiver project, parts provided, will pay $30

[PaulQ]

Greetings, I started on this project a year ago, but my circuit's not working and I need help; using the 12 - 495 pF Russian capacitor (not the 223 pF), huge ferrite bar, and BC548 NPN transistors. I'm following this circuit. Please PM me if we might work something out with turning these components into a functional AM (and below?) receiver. I can mail in US. Thanks in advance.

 

[RFI-EMI-GUY]

Are you using a crystal earphone? Are you sure about the NPN transistor polarity? Have you tried it outside? The coil wire should be enameled not bare as in the Amazon link. The enamel is insulation between windings. remove it with sandpaper at the connection points. Having a larger value variable capacitor will make it harder to tune and it will resonate to a lower frequency when fully meshed.

 

[PaulQ]

Thanks for responding, that's not an Amazon link; it's a link to the schematic.
Yes it's a crystal earphone.
BC548 is NPN.
Yes I scrape/sand the enamel off the wire.
I want the lower frequencies.

 

[RFI-EMI-GUY]

Thanks for responding, that's not an Amazon link; it's a link to the schematic.
Yes it's a crystal earphone.
BC548 is NPN.
Yes I scrape/sand the enamel off the wire.
I want the lower frequencies.

If you click the link for "coil" in the article bill of materials, it takes you to bare copper wire. Thats why I asked.

The transistor markings EBC might be different on the transistor you have. You might want to verify.

The crystal earpiece should give a buzz if you touch it to ground or metal pipe and hold one wire in your hand. It could be bad due to humidity.

That circuit is so basic that it really should pick up a very strong MW transmitter nearby. Can you generate a signal in MW 500 KHz to 1600 KHz somehow?

Try making a "crystal radio using the inductor and capacitor you have as well as a germanium or silicon diode. If it works, your earpiece, coil and capacitor are OK and the problem is within the amplifier.

 

[RFI-EMI-GUY]

Thanks for responding, that's not an Amazon link; it's a link to the schematic.
Yes it's a crystal earphone.
BC548 is NPN.
Yes I scrape/sand the enamel off the wire.
I want the lower frequencies.

If you click the link for "coil" in the article bill of materials, it takes you to bare copper wire. Thats why I asked.

The transistor markings EBC might be different on the transistor you have. You might want to verify.

The crystal earpiece should give a buzz if you touch it to ground or metal pipe and hold one wire in your hand. It could be bad due to humidity.

That circuit is so basic that it really should pick up a very strong MW transmitter nearby. Can you generate a signal in MW 500 KHz to 1600 KHz somehow?

Try making a "crystal radio using the inductor and capacitor you have as well as a germanium or silicon diode. If it works, your earpiece, coil and capacitor are OK and the problem is within the amplifier.

 

[PaulQ]

Thanks again for responding. The earpiece crackles when I turn switch on or off, but no buzz. Maybe I'll just rebuild the circuit. If someone would take me up on offer that'd be great.

 

[majoco]

I would like to have seen a capacitor in series with the earphone - with about 1 volt across it, it's probably biased to one end of it's travel.

How have you laid the circuit out? Many years ago I made my first radio much like yours with brass thumb tacks into a bit of corrugated cardboard and soldered all the joints to the thumb tacks - worked quite well.

 

[RFI-EMI-GUY]

That DIY site seems a bit sketchy as if it is translated by AI or something. I see they have alternate AM receiver designs using BC549 s in two places an 9V batttery.

This circuit is tuned RF TRF design and it appears it relies entirely on the third transistor to act as the detector diode. Not sure how that will work out depending on variables of signal level, bias and transistor parameters.

Also the schematic drawing is a bit confusing in that their are no dots to indicate that lines are to be connected or not where they pass over each other.

I would look for a circuit by Joe Carr or at some other site and rebuild the design. Start with a simple crystal radio circuit with your ferrite resonator variable cap and a germanium diode. If that works, then move on to a TRF.

 

[RFI-EMI-GUY]

I would like to have seen a capacitor in series with the earphone - with about 1 volt across it, it's probably biased to one end of it's travel.

How have you laid the circuit out? Many years ago I made my first radio much like yours with brass thumb tacks into a bit of corrugated cardboard and soldered all the joints to the thumb tacks - worked quite well.

Tracing out the circuit as built and comparing to the schematic might reveal an error in construction.

 

[PaulQ]

Thanks for your replies.
I'll ditch this project and try a crystal set as RFI GUY suggests.
Majoco this project is continued from last year, you were helping on thread which is now closed.
What's a reliable site or J. Carr book where I can get schematics for basic AM radio receivers? Thanks.

 

[RFI-EMI-GUY]

Thanks for your replies.
I'll ditch this project and try a crystal set as RFI GUY suggests.
Majoco this project is continued from last year, you were helping on thread which is now closed.
What's a reliable site or J. Carr book where I can get schematics for basic AM radio receivers? Thanks.

Joseph Carr (SK) published several books on receivers many avalaible new or used on the web. You might try a library and see what you can find in the index.

Otherwise Tuned RF and Crystal radio receivers are found on many websites..

https://en.wikipedia.org/wiki/Tuned_radio_frequency_receiver#Modern_usage

https://en.wikipedia.org/wiki/Crystal_radio

TRF Radios, HAC RADIO, ZN414, MK484

web.archive.org

 

[wtp]

i see the antenna, what about grounding the radio ?

 

[PaulQ]

As advised, I'm redirecting project to an AM crystal radio, grounded to wall outlet screw. I'm following this diagram, with germanium diode, AM loop antenna, and big ferrite bar shown in first post. Please check out my 2 - 495 pF variable capacitor connections (pic attached, diagrammed with white lines) and advise where to make connections. I'm getting a crackle in earphone with various ground and antenna connections (alternately to copper clip, individual and/or linked gang connections etc), and the faintest radio signal, but not distinguishable. Thanks.

 

[RFI-EMI-GUY]

Since your 495 uF variable cap has two sections, you can use 1/2 of it, and obtain 247.5 uf, close to the design specification. Leave the unused portion floating, no connections.

Focus on that weak signal and then optimize the antenna position and ground.
A better article:

Remembering the Crystal Radio

Reminiscing about the good times that crystal radio sets provided.

www.nutsvolts.com