|
|
|
|
|
You can build a sensitive 5-transistor amplified AM table radio with our 10.125 inch ferrite rod, variable capacitor, and circuit template.
Produces loud volume from its powerful transistor audio amplifier. Drives a speaker!
We bet you don't know how to build a radio. The fact is that you and your son or daughter can easily build a working AM radio and learn by doing it!
The analog "feel" of tuning a real radio is virtually forgotten. We are going to change that! You can be one of the "in-the-know people" who actually knows how to build a working radio. You can learn by doing it yourself. We have the circuit plans and top-quality radio parts!
You can amaze yourself and your friends by building a working AM radio! There is a special pride in saying "I built it myself"!
If you have never built a radio before then just start from "scratch" here! Its not a super-het or regenerative, so there are no tricky adjustments or RFI emissions to worry about. You don't need any test equipment to get it working.
Today's digital radio's just can't "cut it" at quickly tuning stations, - zip from the bottom of the band to the top in less than half a second - and allow fine tuning in between stations. Whether you're an "old timer" missing the "quick frequency surfing" that you could do with those older radios, or a "newcomer" you will love using this new radio that you built yourself! Find stations to listen to nearly instantly without waiting for digital numbers to stop and "click in". If you're just longing to bring back the "good ol days" of listening to a real transistor radio then you need to build this 5-transistor AM radio!
This very nice AM portable radio can be built using our 10.125 inch ferrite core rod. This radio will pick up stations loudly without needing any external antenna or ground connections, the sole antenna being the wire wound on the ferrite rod. Station selectivity is refreshingly good for this type of radio as "Q" runs extremely high and separation of adjacent stations 20 KHz - 30 KHz apart is good. This is due to our ferrite rod's exellent electrical properties.
Listen to local stations by day and at night you will hear AM stations from all over the USA without any other antenna than the built-in ferrite rod antenna.
The different functional sections of the radio are shown on our printed card stock circuit template. The radio picks up stations with the tuned ferrite rod antenna (FE-1, L1, L2) and feeds them to a radio signal pre-amplifier transistor (Q1). The radio's RF-amplifier feeds the signal to a transistor audio detector (Q2) that pulls the audio off the radio wave. Transistor Q2 is biased in such a way that it works both as an AM detector and audio pre-amplifier. The audio signal (voice, music) coming out of Q2 is fed to a transistor audio amplifier that boosts it enough to drive a speaker to loud volume on local stations.
This is not some pre-manufactured kit where its all mostly done for you. This is a learning adventure. The challenge is for you to gather all the other parts and actually learn how to build a radio by doing it yourself!
By successfully building this radio you will learn how basic electronic circuits work and how radios are tuned (or how they used to be tuned!!). We've kept it simple using only transistors and individual parts to allow you to learn how basic electronic parts work. The design is simple yet delivers room-filling sound from local stations and at night from distant stations. The radio will receive loudly a 250 watt local AM station 15 miles away, as an example of typical sensitivity. Then at night stations from all over the USA come in loudly.
There is no volume control shown (but you can add one if you want to). Strong local stations come in very loudly, weak stations come in at lower volume. You can control the volume on loud stations by tuning slightly off-channel, or add a volume control. We chose not to as the radio produces good average volume on most stations. The radio does not have an automatic gain control so some learning potential is provided for on fading stations (radiowave propagation) as they get louder and softer directly depending on atmospheric conditions. This is radio as it "used to be" before all the automatic stuff existed!
Because this radio does not have any noise-blankers or automatic gain controls (AGC) you get the pure effect of "open-sounding AM" the way it used to be (and always should be)! At night you will hear the fading AM stations and occasional distant lightning static like your grand-pa used to hear with his AM radio! Build this AM radio and bring back that "good ol' sound" from the good ol' days!
This radio is what is called a "TRF" Receiver, or Tuned Radio Frequency Receiver. It is an amplified "crystal" radio. All amplification is done at the received signal frequency with a single RF pre-amp stage. It does not use any IF (intermediate frequency) amplifiers or RF mixers like modern "super-heterodyne" receivers. The receiver is not a tricky noise-producing "regenerative" unit.
This amplified crystal radio receiver does not generate or produce RFI energy.
The challenge was to make a good AM radio but without using the tricky frequency-conversion circuits or regenerative circuits (or any other circuit that could generate RFI) that are impossible to align without skill and test equipment. The great news is that you can build this radio even if you're new to electronics, and it won't spew RFI.
This radio is very similar to some very early (now antique) AM pocket transistor radios that were produced. Some early AM pocket transistor radios boasted about having only two transistors! This radio has 5 transistors and a much larger antenna so it will perform so much better than those!
See below on this page for some photos and instructions telling how we put our radio together.
THE PARTS WE HAVE FOR THIS AM / Longwave RADIO:
| Part Name | Part Number | Quantity Needed for Radio | Price |
|---|---|---|---|
| AM4 PLANS | | $ 4.00 | |
| FERRITE ROD | | $ 33.75 | |
| 384 pF VARIABLE CAPACITOR | | $ 18.00 |
Add $ 12.00 s/h.
S/H is extra.
Your Quest: The rest of the parts (speaker, switch, battery, battery snap, wire, etc) are common parts that are readily available from electronic parts stores, (such as Radio Shack) or maybe you have them in your "junk box"!
Speaker: Any 4-ohm to 8-ohm speaker will work. We chose to use Radio Shack part # 40-1417 which is a 3.5 inch car speaker with built-in cloth screen grille. Frequency response 300 Hz - 10000 Hz. 5 watts RMS.
Choosing a speaker for your radio: We recommend a speaker of 3 inches to 6 inches. AM stations do not transmit any musical contant above 5000 Hz, so your speaker just needs to go up to 5000 Hz. Large speakers will create louder sound and give the radio a rich BASS tone. Speakers for 300 Hz to 5000 Hz are called "midrange" speakers.
Want a little more BASS from the radio? Change the speaker capacitor "C6" to double the value listed on the parts list. Do not go above triple the listed value, however.
The radio's audio amplifier will reproduce sounds between 20 Hz to 20 KHz. If you don't want to reproduce sounds higher than 5 KHz then change C7 to 0.01 uF.
WINDING THE COIL ON THE FERRITE ROD FOR AM BROADCAST BAND: 530 KHz - 1710 KHz:
Wind L1 and L2 with the number of turns as shown in the close-up photo found in the AM4 PLANS (purchase it above). It is important to space the coils apart as shown in the AM4 PLANS photo so that tuning will be sharp and separation of stations will be good and volume will be loudest.
WINDING THE COIL ON THE FERRITE ROD FOR LONGWAVE BAND: 160 KHz - 500 KHz:
(currently experimental)......
WINDING THE COIL ON THE FERRITE ROD FOR SHORTWAVE BAND: @ 6 MHz - @12 MHz:
(currently experimental)......
The radio circuit itself can easily be constructed on a piece of wood by using our printed card stock template supplied with the AM4 PLANS.
Just place a copper tack (available from any local hardware store) in each dot in the diagram and solder the parts together. We placed the printed paper circuit card onto a small wooden craft plaque of 5 inches by 7 inches, and hammered in all the copper tacks. The parts are supported by copper tacks carefully hammered into the the wood. See close up photo.
Construction may take about 2 hours. It may take longer if the parts won't 'stay still' while being soldered. You may want to tape the part down and solder one lead, then remove tape and solder the other lead.
We built the radio (just the circuit on tacks) in about 2 hours. It worked correctly the first time without any adjustments or troubles. A second day and several more days were spent mounting it all in the box and placing the speaker and mounting the ferrite rod in the box. We used hotmelt glue to attach the ferrite rod to the top of the box. Keep the ferrite rod away from the speaker's strong magnet.
We used hotmelt glue to attach the tuning capacitor to the wood. Be careful to not get hot melt glue into the capacitor's fins, else you will have a mess!
It may take up to 5 to 7 days working an hour at a time to finish the radio completely. Enjoy the building part of it no matter how long it takes you!
To build the radio circuit on the tacks, a 15 watt soldering iron is what you need. Use eye protection goggles (solder or the solder's hot wet flux can splatter). Open a window and use fan ventilation - solder fumes are poison says the fine print. Read all warnings.
IF YOU CAN'T SOLDER, OR NEVER HAVE, (and don't want to learn how today...), Radio Shack stores also have "perforated circuit board" and wire-wrap parts. You can build the radio without needing to solder anything, but we don't recommend it. We did build the radio firstly on a solderless breadboard (just to fool around with it before permanently wiring it) and it worked fine even with the stray capacitance of the metal base it did not squeal or oscillate when built in a "poor way".
IMPORTANT: If soldering, place the transistors lastly. Sit them aside for now.
Refering to parts list and printed card-stock circuit template diagram:
First place and solder all other parts to the copper tacks, starting at part labled "C1" and working toward the right.
An example of how you will be hammering in the copper tacks in first, then placing and soldering all the parts. The circuit diagram on the paper card stock (see price above) shows where to hammer the tacks and where the parts connect. This is a really easy way to build electronics!
You will notice how the transistors are placed with the black case down. Just make sure that "E" goes to "E", "B" goes to "B", and "C" goes to "C". Most transistors have their 3-pins labeled on the case in small letters. If you want to place them with the black case up, you can bend the leads differently than we chose to. If you are adventureous you may want to put in transistor sockets so you can easily replace the transistor should the radio ever get damaged. It is usually the transistor that goes out instead of the capacitor or resistor.
Some parts like capacitors have (-) and (+) markings. Install these correctly else the radio will not work.
The connection points marked with the 3-pronged point all connect together. This is the ground buss. You will need to wire all these points together with a wire as shown above.
Once all other parts and ground buss line is soldered, its time to put the transistors in. Carefully bend the transistor leads as shown above and place transistors with the black case down as shown, allow the leads to lay on top of the copper tacks. Carefully solder transistor leads. Do not allow transistor to get hot while soldering. You should use a clip-on heat sink when soldering transistor leads to prevent excess heat from reaching the transistor's plastic case.
The radio circuit is placed into a wooden box (we bought the box in the craft department at Wal-Mart). We have added front-panel tuning knob and ON/OFF switch and loud speaker.
The finished table AM radio with carry handle (handle found at a hardware store) gives it an antique flare.
The radio works great and looks finished, but we still need to put a border on the front tuning dial and a piece of protective plastic over the dial. We still need to place a back cover on the radio. And we had not yet added the front panel decorative handles at the time this photo was snapped.
We calibrated the tuning dial by tuning the radio's tuning knob and allowing the signal to peak on a nearby digitally tuned AM radio from the "tuned ferrite-rod antenna effect".
The calibration sheet was pulled off and scanned into a computer, then loaded into a photo/paint program and re-touched and re-drawn.
The new dial was printed on card-stock and was glued down using Elmer's glue, and it was also coated on the front with Elmer's glue which will slightly smear the ink-jet print to make it look more "antique-ish".
You will have to print and make your own tuning dial out of card-stock or an ink-jet printable transparency sheet, or just use a fine pen or other instrument and hand-mark the wood directly!
Perhaps your grandparents or great-grandparents built their own radio during the early days of radio. Now you can do it too!
The wooden box with drill points marked. From left to right: Tuning capacitor, ON/OFF switch, Speaker.
We first considered drilling out the large circle for the 3-inch speaker to fit directly into, but thought it better to design a grill template and drill many small holes to act as a grill for the speaker.
The holes are drilled. The paper speaker hole template (see below) that we made was placed and the holes are drilled out. Don't forget to drill the 2 holes to mount the speaker, and make sure that the mounting holes are not too close to any other drilled holes lest the speaker could come dislodged.
Specifications: Current draw when idle between stations: 34.78 milliamps at 9 volts.
When powered up, the radio should draw approximately the current level listed above.
Click Here to view the AM dial front panel we made. Scroll over because it is large! Right-click and save. It is the right size to print out and use on your radio, if you don't want to hand-calibrate it yourself. The numbers may not match your radio's tuning range exactly.
Here are two designs for speaker grilles. We drilled through the front panel wood and mounted the speaker behind the grill. Takes a lot of time to drill the holes but its better than cutting out a large ugly circular hole to mount the speaker.
We used the square design.
You may choose to use your own design you make on a paint program on your computer. Make sure the grille is big enough for your speaker and that you have a minimum of 100 holes for the sound to go through.
Make sure to put a back cover on your radio and drill a few holes in the cover so the sound can come out the back too. This makes the radio's volume even louder and adds "richer" bass tones. You may want to experiment with different back covers and sound port-holes or speaker mounting or sound wave-guides to get the exact "custom" sound you want. Its your radio. Build it how you like it!
We had no trouble building the radio. The radio worked from the start without any squeeling, hissing, or other electrical problems.
Start with a brand new 9-volt battery. As battery ages the volume will become lower so start out with a fresh battery!
You can check the various stages of the radio as follows:
Touching C1 if the L2 coil is NOT connected will produce a loud buzzing sound. This is normal, but will never occur once the L2 winding is connected.
Touching C2 causes a buzzing noise from audio hum. This is normal.
Touching C4 causes a buzzing noise from audio hum. This is normal.
The audio amplifier requires use of the resistor and capacitor values listed, else it will not work correctly. Do not leave out any parts!
There are both PNP and NPN transistors used in the radio. Make sure you carefully place the "E", "B", and "C" leads of the transistor types to the correct tack points of the circuit diagram. Don't mix up your transistors!
Strong local stations may cause overload or background reception. Rotate radio to null out the strong station. The zero-point null is sharp.
Do NOT ground the L1 coil to the ground buss. Let the L1 coil "float" as shown.
Make sure to wind the L1 and L2 coils as shown in the photos. Make sure that the tuning capacitor's metal frame is connected to the end of L1 that is closest to the L2 winding. Make sure that the grounded side of the L2 winding is closest to the side of L1 that is connected to the tuning capacitor's metal frame. See above photo of inside radio.
Very poor reception? Did you mount the ferrite rod horizontally like shown? Don't mount the rod vertically else it will not pick up any stations!
Receive several stations at once during daytime? (NOTE: At night this is normal at night when many strong stations overlap). Is L2 placed too close to L1? It should be 1 and a half inch, or even 2 inches down away from L1. Try less turns for L2 to improve station selectivity. Move L2 up to 2 inches down away from L1.
Receive some stations but not others? Rotate the radio 90 degrees to face a different direction.
The dial on your radio shows 2500 KHz. Does this mean it will hear WWV? It will tune 2500 KHz, but have not heard WWV yet.
Hard to tune? Tune very slowly and listen for the sound to get the loudest from the speaker. Don't use a metal tuning knob. Use a plastic tuning knob. Rotate radio for loudest sound from the individual tuned station if needed.
Connecting an outdoor antenna? Wrap 5 or 10 turns of wire around the radio's case and connect to a 50-foot long wire and a ground rod.
Local station is too loud! Power the radio on 6 volts instead of 9 volts or add a 100-ohm volume control resistor in the speaker line.
Poor sensitivity if all else checks out? Is the ferrite rod too close to the speaker's magnet? Mount speaker and ferrite rod at least 3 inches apart. See photos above.
Poor sensitivity if all else checks out? Check the transistors, especially Q1.
Want something a little different?
Want even better reception? No doubt other transistors than those supplied can be substituted that will slightly improve performance and sensitivity. We may make these parts available, extra, upon discovery. Have fun playing.....and playing with... your AM radio!
Peaking it out to the max? Still working on it. Just looking for the top optimum performance to squeeze that last ounce out like all radio buffs do.....We'll let you know what we find.
The radio can be easily modified to tune lower in frequency (the longwave band). Just add more turns on the "L1" coil. We're working on a longwave only unit....
Can I convert the radio to shortwave? Not as easy as it sounds. We're working on a shortwave only unit.
You can easily add a VU meter (sound level meter) directly across the speaker terminals with a 1N3600 germanium diode and any VU meter movement (50 uA should work) and a limiting resistor (to keep the meter from pegging out on the loudest stations).
External antennas: You don't need an external antenna to use this radio, but one can be connected to the L1 coil. Connect a ground to the radio's ground terminal. The radio was designed to not need an external antenna and may receive lots of noise if one is used.
Be careful how you mount the ferrite antenna rod. If you want to change it later, don't hot melt glue it to the wood because it may prove very hard (or impossible) to remove.
To tune lower in frequency (longwave) wind more wire on the ferrite rod for L1. Use # 26 magnet wire.
Don't want the radio to be so loud? Power it with 3 "AA" batteries (4.5 volts) instead of 9 volts.
DO NOT POWER THE RADIO WITH MORE THAN 9-VOLTS!!!!! If you want free power for your radio try a 9-volt solar panel.
WARNING!: THIS RADIO DOES NOT HAVE A VOLUME CONTROL SO DO NOT LISTEN THROUGH HEADPHONES OR AN EARPHONE. SUDDEN VERY LOUD SOUND IS POSSIBLE! USE SPEAKER ONLY!
Love the 1-of-a-kind AM radio you built? Take a photograph or two of it and write us a little about your experience (and the most distant AM station you have heard with it) and snail-mail them to us and we may scan the photos on our web site here (web link).
Speaker Grille Templates you can print and use.
TROUBLES?
CHANGES AND MODIFICATIONS:
Do not use an AC adapter!!!
This device may not cause harmful interference, and must accept any interference received, including interference that may cause undesired operation.
This amplified radio receiver device does not generate, create, or emit radio frequency energy. RF generation is not used in this amplified crystal radio device.
Ferrite rod antenna components exibit a bi-directional reception pattern as shown above. Rotate radio for best reception.
Looking down from above with the ends of the ferrite rod pointing North and South, just like a compass would, the directions of best reception are EAST and WEST as shown by the circles in the chart above. There is no signal pickup from the North or South. To pickup from the North and South you would have to point the ends of your ferrite rod to the East and West.