Introduction: Three Transistor Short Wave Radio

Picture of Three Transistor Short Wave Radio

The 60's and 70's were the golden age of electronic kit building. The novice had a great many educational kits to choose from that taught basic skills and electronics theory while assembling a device that could do something useful or entertaining. An advanced builder could use "sweat equity" to inexpensively obtain popular electronic products like HiFi stereo systems, color televisions, CB radios, and automotive test equipment.

Today there are still quite a few electronics kits available for education purposes, but rapidly evolving features and shrinking components ended the consumer electronics kit business. I would have loved to have assembled some of the products that were popular in the 70's, but unfortunately most of the companies that made all those wonderful kits were gone when I began my career. In honor of a great set of educational Radio Shack electronics project kits available during the 60's and 70's, I've redesigned the original Science Fair brand Three Transistor Shortwave Radio (Catalog #28-110) using modern components still available from electronics component re-sellers in the US. All of the components in the updated kit can be found on Amazon. There were many things Radio Shack did extremely well during its prime. For the nostalgic or the enthusiast who would like to build an updated version of this classic radio I've included schematics, parts information, assembly documentation, and pictures of a completed and tested Three Transistor Short Wave Radio based on the original from 1968.

Visit for more information!

Step 1: Obtain the Assembly Manual

Picture of Obtain the Assembly Manual

The Three Transistor Short Wave Radio project described here is based on the Radio Shack pbox kit of the same name, but it has been updated with silicon transistors and passive components and controls that can be obtained from electronics suppliers on Amazon. I've built the updated radio kit described here and believe it works just as well as the original kit did back in 1968. To make it easy to replicate my work, I've provided illustrations and step-by-step assembly documentation based on the original assembly manual from Radio Shack.

To build the radio, you will need the revised assembly manual available here.

I've kept the original branding and publishing style of the Science Fair Three Transistor Shortwave Radio in order to preserve the original look and feel of the documentation set for the builder. But every page has been updated to reflect the changes I've made in order to incorporate modern and available parts.

Step 2: Obtain Components Listed in the Assembly Manual Parts List

Picture of Obtain Components Listed in the Assembly Manual Parts List

Review the parts list and obtain the components indicated. Everything but a few pieces of hardware are available on Amazon or can be obtained directly from the suppliers indicated at the bottom of the parts list.

Below are a few notes regarding the parts used for the radio:

  1. The transistors for the radio can be purchased from Amazon or Radio Shack (assuming they are still in business in your area). I highly recommend the excellent Joe Knows Electronics semiconductor kit. It includes the transistors you need for this radio project and over 150 different types of transistors and diodes for just $22. And it includes a set of documents that are really good reading for the beginner. Check out You will not be sorry.
  2. The resistors for the radio can be purchased from Amazon or Radio Shack. Radio Shack has a good selection of 1/4W resistors in a big 500 piece bundle for about $15.00 if you have a store nearby. Joe Knows Electronics also has a nice 800 piece package of 1% resistors for $12.00 if you don't mind ordering online. Joe's is a really good and well organized kit even if 1% resistors are a bit of tolerance overkill for this radio project.
  3. I strongly recommend ordering NP0 ceramic disk capacitors from Mouser or Digikey as they will far outperform most anything you can get on Amazon. The Joe Knows Electronics capacitor kit is an extremely good buy for every other capacitor at 645 pieces for $13.00. Don't bother with Radio Shack for capacitor kits as they are mostly junk values you will never use.
  4. I purchased several crystal earphones from AmplifiedParts on Amazon and they work great despite the poor reviews. Whatever quality problem they had in the past seems to have been ironed out. The crystal earphone comes with a 1/8" mono phone plug so I added a 1/8" mono phone jack from Radio Shack. The phone jack is also available from various sellers on Amazon.
  5. The variable capacitor (and a lot of other rather old and interesting parts) can be found at Uxcell (via Amazon) which seems an unlikely domain for radio stuff but they do have a lot of radio stuff that's interesting. I've created a diagram of the variable capacitor here that will help you figure out how to wire it in the radio.
  6. The case for the radio I built is a Hammond 1591GSBK ABS Project Box from with a piece of vector breadboard cut to fit on the top and spray painted with high temperature automotive flat red. I like the look of red on black, and the red color of the breadboard matched the red color of the original pbox kit. It's completely up to you how you want to house and color the kit you build.
  7. The knobs I used are Radio Shack knobs I've had in inventory for decades. Use anything you think is cool that will fit on the pot/varicap shafts.
  8. You will need to be creative on how you mount the variable capacitor on the vector board. I used a piece of 1/32" sheet metal cut to size with a Dremel tool grinding wheel and then drilled the holes to mount the variable capacitor with a power drill. Then I bent the end of it 90 degrees to form an L shape.
  9. You will need to be creative on how you mount the tuning knob to the variable capacitor. The shaft on the varicap is only about 1/4" long so you will need something to extend it. I found a plastic cylinder with a hole drilled through it that was about 1" long at my local Ace Hardware store. They have a really nice selection of odd hardware that is very useful.
  10. The 2-position barrier strips are available from Amazon or from Radio Shack in a pack of four. These are a great value at the price so if your local Radio Shack hasn't yet been turned into a Sprint cell phone shop you should definitely buy all of the packs on the peg. I know I did.

Step 3: Review the Schematic to Become Familiar With the Radio Design

Picture of Review the Schematic to Become Familiar With the Radio Design

The Three Transistor Short Wave Radio is composed of 4 major building blocks:

  1. Tuner - Selects a station from the band of frequencies the radio can receive.
  2. RF Amplifier - Amplifies the audio modulated carrier selected by the Tuner.
  3. AM Detector - Strips off the RF carrier leaving the original audio signal intact.
  4. AF Amplifier - Amplifies the audio signal so it can be heard on the earphone.

Variable capacitor C5 and tuning coil L1 comprise the Tuning section. L1 is a fixed inductor wound according to the Assembly Manual for the frequency band of interest. Stations are selected by rotating the variable capacitor.

The RF Amplifier/AM Detector section is actually a Colpitts Oscillator with an added variable resistor R2 that serves as the regeneration control. Resistors R1 and R4 provide base voltage to Q1 so that it's collector is fixed at approximately 3V. This collector voltage was chosen so that the RF Amplifier/AM Detector will continue to operate properly as the 9V battery reaches the end of it's life. The large values of R1 and R4, and the bootstrap bias configuration they are connected in, were chosen so that the RF Amplifier/AM Detector will have a high input impedance which improves the selectivity and sensitivity of the radio. Capacitors C1 and C6 were included to bypass RF around resistors R1 and R5 respectively which improves the gain of the RF Amplifier circuit. The collector output of Q1 is fed back to the emitter of Q1 through capacitors C2 and C3. Normally this positive feedback would cause the RF Amplifier/AM Detector to continuously oscillate. However the regeneration control provides an adjustable amount of negative feedback at the emitter of Q1 that counteracts the positive feedback. By carefully adjusting the amount of negative feedback on the emitter of Q1, the circuit can be made to provide extremely high gain just before oscillation occurs, and at the same time remove most of the RF Carrier signal and the unwanted image of the audio signal. This behavior is the reason the regenerative radio works so well.

The AF Amplifier is a simple two-stage direct coupled Common Emitter amplifier for driving the crystal earphone. Transistor Q2 provides a gain of approximately 5 and together with R10 and C9 performs additional filtering of the carrier signal. Transistor Q3 provides a gain of approximately 100 (the transistor current gain at .5mA). Capacitor C11 is provided to bypass audio frequencies around resistor R12 and improve the gain of Q3. Together, Q2 and Q3 provide an additional gain of approximately 500 after the RF amplifier. The value of R12 was chosen so that the collector voltage of Q3 would be set at approximately 1/2 battery voltage which ensures that the Detector and AF Amplifier will continue to operate properly as the 9V battery reaches the end of it's life. Capacitor C7 and resistor R6 are wired together as a simple RC Low Pass Filter to prevent RF noise at the RF amplifier from bleeding into the AF amplifier via the battery connections.

Step 4: Review the Circuit Board Layout

Picture of Review the Circuit Board Layout

The Assembly Manual provides a step-by-step checklist for installing and soldering each component to the vector board. As you can see from the opposite side illustration of the vector board, I've used point-to-point wiring with 20 AWG solid hookup wire. Most of the connections can be made with just the component leads. But power, ground, and signal bus leads are best done with lengths of hookup wire. Parasitic capacitance isn't much of an issue for the frequencies this radio will operate at and I've already compensated for most of these in the redesign. When built, the radio is free of unwanted oscillation or noise.

When it comes to wiring, try to be as neat as I've indicated in the assembly manual. You don't have to be the world's best soldering artist but there's no good reason to do the work half-way. Go all out and make your radio look as good as you can.

Step 5: Follow the Steps in the Assembly Manual to Complete the Radio

Picture of Follow the Steps in the Assembly Manual to Complete the Radio

Before you begin:

Cut the vector board to closely fit inside the top of the Hammond project box. Measure the lengths needed and try to line up the edges along a row of holes if possible. With an Xacto knife, score a line into the vector board deep enough that it can easily be felt with a fingernail. Then carefully break the board apart along the score line.

Using an Xacto knife or low speed power drill, cut the holes for the Hammond mounting screws to line up with the mounting holes in the Hammond project box.

Using an Xacto knife or low speed power drill, cut the holes for the variable capacitor mounting bracket.

Using an Xacto knife or low speed power drill with a reaming bit, cut the holes for the potentiometers R2 and R7, and the hole for the phone jack.

If desired, spray paint the top of the vector board in flat red. Or any other color you wish. The natural vector board finish also looks nice.

After the paint has cured, follow the step-by-step instructions in the assembly manual.

Step 6: Assembly Photos - Mounting the Terminal Strips

Picture of Assembly Photos - Mounting the Terminal Strips

After Assembly Step 3, the radio should look something like the photo above.

Step 7: Assembly Photos - Mounting the Radio Controls

Picture of Assembly Photos - Mounting the Radio Controls

After assembly steps 4-6 the radio should look something like the photos above.

Step 8: Assembly Photos - AF Section Completed

Picture of Assembly Photos - AF Section Completed

After assembly step 35 the radio will look something like the photo above.

Step 9: Assembly Photos - RF Section Completed

Picture of Assembly Photos - RF Section Completed

After assembly step 49 the radio will look something like the photos above.

Step 10: Assembly Photos - the Completed Three Transistor Short Wave Radio

Picture of Assembly Photos - the Completed Three Transistor Short Wave Radio

The L1 coil winding chart explains how many turns of 20AWG insulated wire to use for the frequency band of interest. The terminal strips make it easy to swap the coils as needed during a listening session.

Any radio is only as good as it's antenna and the environment it is in. In my area, everyone has a wireless router, several cell phones, LCD TV's, and many other devices that make lots of electronic noise. A good antenna as described in the Assembly Manual is essential for getting the best performance from this radio project.

After building the radio I've successfully received WWV on 5, 10, 15, and 20 Mhz with good copy. I've picked up all the well-known short wave KW transmitters from around the globe. And I've picked up SSB on 7Mhz and 14Mhz. SSB can be received but the detector is not designed to clearly demodulate it. But if you thought the Probe Droid from Star Wars sounded cool, definitely tune into SSB with this radio.

I'm extremely happy with how the 3 Transistor Short Wave Radio looks and how well it pulls in distant stations

I hope you have as much fun working on this project as I did. Good luck and good listening!


SHOE0007 made it! (author)2017-07-29

Equiv to three transistor radio for this kit.

SHOE0007 (author)2017-07-06

Kit of VHM and AM radio just ordered.

SHOE0007 (author)2017-02-04

Here is image of it in action with 9 volts not 3 volts!

SHOE0007 made it! (author)2017-02-04

Here some diagrams of IC op amp from the 160 in 1 and a radio video. No copy right conflict intended.

SHOE0007 (author)2017-02-04

Very interesting. A small IC like a single OP amp can amplify sound more effectuvely than 3 transistors. In fact IC radio with three transistors in it works like that.

netzener (author)2016-06-12

I've received a few requests to see if it's possible to resurrect the old Science Fair Globe Patrol 4-Band BC/SW radio, an example of which can be found at the URL below:

I've determined that it is feasible to construct a receiver using a similar RF design but with the following changes:

1. The tuning section will use different component values in order to make use of the same variable capacitor specified in the Three Transistor Short Wave Radio.

2. The band spread capacitor will be replaced with a 1N4001 diode tuning capacitor. I could not find a volume reseller for the 12pF band spread variable capacitor.

3. The RF transformers are no longer available from any source so I've redesigned these using hand-wound toroid core inductors and 30AWG magnet wire. These aren't all that fun to wind by hand but they work really well.

I really don't like the transformer coupled audio amplifier in the old design. I think it's inefficient and just not all that good. But it is possible to replicate it with transformers still available. I could redesign the AF stage with a direct coupled transistor amplifier. Or just use the well-known LM386 with a gain of 200. If anyone has a strong opinion on that, let me know.

I've constructed and tested a rough prototype for the broadcast band which seems to work well. It tunes 550Khz through 1.6Mhz. The diode "varactor" band spread seems to work really well for tuning above and below the center frequency. It's range is currently +/- 45Khz at 1Mhz. A photo of the prototype is shown below.

When I get the design into a state in which someone else can build it, I'll publish an article on it.

smirnoff46 (author)2016-06-01

Nice project. I remember getting a Radio Shack kit when I was young and found myself years later wishing I knew what happened to it. I'm pretty sure I was picking up air traffic control communications at the time. I recently tried to make a shortwave/VHF radio following instructions from a Youtube video, but I haven't been able to get it to work. Not sure what I did wrong but the instructions were not very clear. I would love to try your design, but can you tell me if it would work with powered speakers instead of the crystal headset, or would that feed back power into the circuit? How could I prevent that? I like the idea in the other design of using a 9v battery in order to be able to use regular headphones or plug into a computer to make recordings. Thanks for any suggestions!


netzener (author)smirnoff462016-06-01

The output of the 3 Transistor SW Radio is designed to drive a high impedance crystal earphone, but it is possible to attach an external amplifier to drive a speaker. As long as the external amplifier input impedance is around 20K Ohms, there should be no problem driving a speaker or set of dynamic headphones.

If you would like to build your own amplifier, download the LM386 IC data sheet from TI at:

Construct the "Amplifier with Gain = 20" on Page 6 excluding the 10K volume control. Attach Pin 3 of the LM386 to the earphone output connected to Q3 and the amplifier ground to the earphone ground. The amplifier can be powered from the same 9V battery used to power the radio.

The input impedance of the LM386 is 50K Ohm which is perfect for the output of the radio.

Thanks for the kind comments and I'm glad you liked the article.

Let me know how things go for you should you decide to build the radio.

Thanks again!


smirnoff46 (author)netzener2016-06-05

Thanks for the reply and advice. I'm currently collecting the parts list from Mouser. It's been a bit of work narrowing each part down to the right specs from the thousands of results you get from each part search, but I'm fairly confident in my choices up until the Mylar Capacitor. They seem to be calling it by a different name. Will this one work?:

Also, I'm assuming the voltage rating on the capacitors and resistors is not so critical. Am I correct in that assumption? I'm finding parts ranging from 1kV to 500V. I'm trying to stay at the smaller end, and away from AC ratings. Is that good enough? Thank you again sir.


netzener (author)smirnoff462016-06-05

You are absolutely correct that voltage ratings in this project are not critical. For capacitors in general, lower voltage means smaller size. A 50V rating with 5% or 10% tolerance Polyester Film (Mouser 647-QYX1H104JTP) will work just fine. I should probably have used the correct name for the capacitor dielectric material. Mistake on my part I think.

In this project the voltages are very low so anything above 15V will last.

Most common coupling capacitors today start at around 50V and go up from there. I find that the 50V variety are pretty cheap and are small enough to fit the layout.

Aluminum electrolytic filter capacitors, however, can be rated all the way down to 4V which are typically only used for 3V power in digital circuits. Electrolytics with 16V, 25V or 50V ratings will work just fine.

Resistors can be 1/4W or 1/2W and are large enough to easily work with on a breadboard. Current consumption is very low so even 1/8W will work but those are tiny and their leads are fragile.


smirnoff46 (author)netzener2016-06-06

Thanks again for the info. Sorry to keep bugging you, but I now have everything sitting in the cart on Mouser except for the 140pF Variable Capacitor. I'm not clear on if I need to find something labeled exactly 140pF (which Mouser doesn't have) or if I can get anything that has 140 in the range? For example: 10pF to 150pF, or 12pF to 180pF. Once I get that out of the way I'll be ordering and starting the build as soon as everything is shipped. Thanks so much for all your help!


netzener (author)smirnoff462016-06-06

Not bugging me at all. Glad to be of some small assistance to you.

I would recommend the variable capacitor from Uxcell ( available from their web site or on Amazon. Last time I checked neither Mouser or Digikey carried these.

The Uxcell part number is a13091000ux0626. It's $6 for two plus shipping. I've ordered quite a few items from Uxcell and their shipping is very quick for items in stock. Items they have to order internationally take longer. The variable capacitors I ordered took only a few days. The only challenge is extending the capacitor shaft so that a suitable knob can be attached. I usually look for something in the junk box that can be made to work.

The description states 20pF - 126pF but in my measurements the capacitance is a little higher than published and there is a trimmer on the back that can be used to increase capacitance by 10pF. I didn't have to use the trimmer. It worked great out of the box.


smirnoff46 (author)netzener2016-06-09

Just one more question. Is there something on Uxcell that would work for the 0.047uf multilayer capacitor? I can find .047uf and I can find MLCC's, but not in the same product at once. I've already placed my order with mouser and I'm trying to keep shipping to a minimum. Unless Mouser has a 140pf Variable capacitor that I could use, I will have to place another order with mouser and one with Uxcell. Thanks again


netzener (author)smirnoff462016-06-09

No problem. A 0.047uF capacitor can also be stated in nano-farad units or pico-farad units. So 0.047uF can also be referred to as 47nF or 47000pF.

I used a MLCC (Multi-Layer Chip Capacitor) because that was what was in my Joe Knows Electronics Capacitor Kit. But you can use almost any small capacitor type such as ceramic disk or polyester. Capacitor type isn't critical.

Uxcell offers an MLCC capacitor via part number a14070900ux0094.

They also offer a polyester capacitor via part number a14062700ux0358.

I like the polyester capacitor the best because it is closest to the original design and has much longer leads for you to work with.

The only thing is... Uxcell doesn't sell these in small quantities. It's around $6 for 50. But you might be able to use them in other projects in the future. It's always nice to have extra.


jclassic1 (author)2016-06-09

This is probably one of the best shortwave radio projects I have found.

I have built AM and FM radios but it is shortwave that interest me the most.

I have just ordered the transistors as they are a type that I don,t have.

I may build it dead bug style instead of using the perf board or vero board here in the UK.

Great article ,I hope you do some more

All the best


netzener (author)jclassic12016-06-09

Many thanks for the comment and I'm glad you enjoyed the article. Dead bug style on single-sided PCB will work really well. Probably better than the perf-board for hand capacitance.

I can't take full credit for the design and layout as that was originally a product of Radio Shack in the US. But it was a lot of fun redesigning the radio to use parts still available from retailers.

Thanks again for the very kind comment.


Iansteward (author)2016-05-02

I have just built this and will be testing over the next few days. Very nice instructions. Can you confirm any issues if I were to use a pcb instead of Veroboard.?

Ian Steward

netzener (author)Iansteward2016-05-02

Should work great with PCB instead of Veroboard. Let me know how it goes for you and send a picture if you can.

I've had good results in the evenings and excellent results when I get away from the buildings I live nearby (noise from WiFi routers, LCD TV's, and computers).

Tuning and Regen require some practice as hand capacitance at the tuning knob and earphone cable shift things a bit. But once you get the hang of it, it's pretty easy to tune in stations.

I've had good results adjusting the Regen control until a hissing sound occurs (can be quite loud with some buzzing so use caution with the earphone). Then when tuning I listen for a "birdie" sound similar to the sound effect TV shows seem to like to use when characters are tuning a radio. Then I back off of the Regen control just until the hissing stops (which stops the birdie sound as well) and rock the tuning capacitor back and forth. Sometime I get a station with audio, sometimes I get telemetry broadcasts or other digital transmission. I then repeat the process until I hit a station with voice or music. Many times I can just continue tuning and slightly adjusting the regen control and easily get another station.

It's "fiddly" and sensitive but satisfying all the same.


Iansteward made it! (author)netzener2016-05-04

Thanks for the your input on tuning. I did finish the radio and I am testing. I do pick up some stations during the day (I liv e in NH about 5 miles from Manchester) and at night I pick up lots of stations. My Antenna and Grounding is temporary for now and I am using house earth and a 25 foot wire across the room. I am trying to confirm the frequency ranges for each of my coils (2, 8 and 25 turn with 20 awg insulated wire). It is very sensitive and station signals can vary in and out. However I am excited on the results so far. If you have further advice on the best way to confirm station frequencies the would appreciate it. Photo is attached.

Thanks for your help on this.

Ian Steward

netzener (author)Iansteward2016-05-04

Wow! Excellent work on your radio project. Looks great. Many thanks for the status update and photo. I'm very happy that the results are exciting. That's awesome. And with a 25' indoor random wire antenna no less. Very cool! A customer of mine is in Waltham, MA and I fly in/out of Manchester International from Austin to visit them. The drive to Manchester is more fun and I like the airport better than Boston Logan. I've wondered what reception would be like so close to the Atlantic.

A good start at determining what frequency you are tuned to is to attach a coil that can reach one of the following frequencies:

2.5Mhz, 5Mhz, 10Mhz, 15Mhz, 20Mhz

The NIST operates a station in Fort Collins, CO with call sign WWV at these frequencies that is always broadcasting time information in the form of clock tones every second followed by a voice announcing the time. When you hear these tones, you know you have found one of the above frequencies.

Once you have a starting frequency, a marker generator will help you find any frequency above and below. A simple marker generator usually consists of a square wave oscillator at a fixed fundamental frequency like 100Khz. The harmonics of the fundamental produced a set of marker frequencies all the way into the RF bands every 100Khz. These marker frequencies act like the scale on a radio dial. There are quite a few marker generator circuits described on the web and how to use them. It's a simple process once you get the hang of it. I've used marker generators to create a calibrated dial for a radio that didn't have one.

An example of the process goes like this: Install the 25-turn coil and rotate the tuning capacitor until you hear the clock tones of the WWV. That station is at 10Mhz. Now that you know where 10Mhz is, turn on the marker generator. You should hear what sounds like radio interference which is the marker generator frequency "beating" against the WWV radio frequency. Adjust the Regen control until you hear a hissing sound and then carefully tune down from WWV. As you tune you will encounter a whistling sound that changes frequency as the tuning capacitor is rocked back and forth. This is 100Khz below 10Mhz, or 9.9Mhz. Continue tuning down until the next whistling tone is heard. This is 200Khz below 10Mhz, or 9.8Mhz.

The above process can help you bracket the station of interest in order to estimate it's frequency. But it can be tedious to do every time. But this process can also be used to create a dial for each coil in the radio, which is a more permanent solution.

Hope this helps. Others in the forum may want to contribute their experiences tuning a radio without a dial.

Let me know what you find out!


Iansteward (author)netzener2016-05-05

Thanks. This is great and I will try this procedure over the next week. Yesterday I did come across the WWV station very clearly. Thanks for taking the time to help with this.

Iansteward (author)Iansteward2016-05-09

I will be building my own 100khz marker generator from a circuit I saw on the web. This does not give any instruction on whether I need a probe(or just wire) for the output. Generally how do you interface the generator with the SW radio. Sorry I am a novice on this stuff.

netzener (author)Iansteward2016-05-09

No problem at all. I just use two short pieces of insulated wire around 12" (30 cm) each. Trim about 1/4" (6 mm) of insulation from one end of each wire. Connect the stripped end of one wire to the Antenna connection on the radio. Connect the stripped end of the other to the marker generator. Then lightly twist the two wires together. The capacitance between the insulated wires is enough to couple the marker generator energy into the radio. If you find that the 100Khz fundamental overloads the radio (constant noise no matter where you tune), unwrap the wires some until the radio tunes normally. If the harmonics cannot be received, wrap the wires more tightly.

You may find that just having the wires near each other, or laying loosely on top of each other, rather than wrapped will work. That's OK too.


DHeigh (author)2016-05-03

Thank you.
I have been regretting not buying a "Globe Patrol" when I was younger for decades. I love the portability of the design (small case & battery powered).

Please consider using a low-profile case, similar to the cases Ramsey kits uses for their SW kits. It might make a good update - especially for campers like myself.

DHeigh (author)2016-04-30

Can you do anything about resurrecting the "Science Fair "Globe Patrol" regenerative radio"? It was more complicated, but more capable too.

netzener (author)DHeigh2016-04-30

Oh, yes. Great question. It will not be difficult to redesign the circuit using modern parts. I've been thinking through the easiest way to replicate some of the coils and assembly steps. And I've been reviewing manufacturers of multi-position rotary switches to see how close I can stay to the original design. Instead of air variable capacitors, I can refactor the design to use varactor diodes and potentiometers. That would give the finished radio a similar look and feel, but varactor diodes are mostly SMT components these days which are hard for the average builder to solder. The challenge is making sure that the parts I specify will be available for at least 3 to 5 years so that folks who are interested in building the radio won't be disappointed by unobtainable or hard to handle components. The other challenge is making sure the project doesn't turn out to be so complicated that folks would rather just read about it than try to build it themselves.

But yes, I am very interested in seeing the Globe Patrol radio or something very much like it making radio sounds again.


StaceyCope (author)2015-10-20

hi @netzener I am considering building this as a physical accompaniment to a paper i'm writing on diy radio making culture (past & present). Could you tell me if this variable capacitor would work for this project? I'm hoping to buy everything i need from one source.

StaceyCope (author)StaceyCope2015-10-20

Woops the url got cut off.

netzener (author)StaceyCope2015-10-20

Could you send me the Digikey part number? The URL displays "Page Not Found" due to limitation on the length of a URL in the comments section.

StaceyCope (author)netzener2015-10-22

Oh okay this is the part number: SG3014-ND

netzener (author)StaceyCope2015-10-22

That part number refers to a small trimmer capacitor. It's less than 1/4" in diameter and adjustable only via a small screw driver. Trimmer capacitors aren't suitable for tuning capacitors as they are too difficult to adjust over a broad frequency range and they aren't designed to be rotated frequently. Trimmers are typically used for fine-tuning in combination with a tuning capacitor that does the course-tuning.

The last time I conducted a search, none of the volume distributors carried an air variable tuning capacitor of the type described in this article. The modern designs they sell parts for use semiconductors (varactors, PLL's, etc) for fine and course tuning.

The specialty electronics retailer is the best place to obtain components no longer commonly used in a radio design. An Amazon search for "2pcs 443DF 20-126pF Medium Variodencer" will reveal the product needed.

Also keep in mind that the specialty retailer is the best place to find the crystal earphone. The dynamic earphone commonly used with cell phones and MP3 players will not work for the radio design presented in the article. An Amazon search on "Crystal Earphone" will reveal parts of the type needed. There are a number of customer complaints regarding reliability for the parts on Amazon. I purchased a similar earphone through Amplified Parts ( using part number P-A480 and experience no quality issues.

If you have any questions or need assistance, just let me know.


StaceyCope (author)netzener2015-12-01

Hey @netzener i've been working on this awesome radio and i noticed one confusing thing in the instructions. step 23 says to connect the positive lead of C7 (47uF elec capacitor) to R6 (2.2K resistor) but then step 29 says to connect the positive lead of C7 to R7 pot lug C. in your photos it looks like the neg is soldered to R6. clarification greatly appreciated!

netzener (author)StaceyCope2015-12-01

Good catch! Step 23 should have said "...Connect the NEGATIVE lead of C7 to resistor R6
as shown in Fig 1 and solder all leads and wires together."

To clarify:

The NEGATIVE lead of C7 should be connected to R6.

The POSITIVE lead of C7 should be connected to potentiometer R7 lug C.

I'll correct the documentation. If there is anything else you find that doesn't seem right, please let me know and I'll fix it. Thanks for the feedback.


sky_jim (author)2015-07-10

When I was a struggling college student I used that receiver as virtually my only form of entertainment for a while. Fiddling with those coils and tweaking the regeneration was addictively tedious. I think it lit a fire that led to my ham license.

3of5 (author)sky_jim2015-08-23

It was hombrew AM radios and a heathkit hw-7 that lead my to get my license, still waiting to upgrade to General this October. What does your callsign happen to be? You can look me up on under kd9bwi.

netzener (author)sky_jim2015-07-11

I was the same way. I built a few AM crystal radios and was disappointed that I couldn't tune in a single station without a good antenna. Then I tried this regenerative radio and was delighted with what I could pick up with a 10ft wire antenna hung from the ceiling. And even more delighted with what could be received with a good antenna and ground connection. After finishing the radio redesign, I am constantly trying different coil windings to see what it will do. That can certainly be addictive.

As a side note to folks reading the comments in this article, the ARRL reports record numbers of ham license holders and record numbers of new applicants for the three different ham license levels in 2015. Over 700,000 people are active in the amateur radio sciences in the US. Numerous Scouting and STEM clubs have included radio technology in their programs. The ARRL is politically active at both the state and federal level obtaining better operating rules and more frequencies on which to broadcast. Local and state governments acknowledge that ham radio volunteers perform a vital communications service during disasters and in remote locations where cell phones do not work.

Some years ago I thought amateur radio had faded away but I was wrong. To see for yourself how active things really are, subscribe to the email newsletter from your national amateur radio organization (in the US that would be Download a free study guide and in just few weeks you will be ready to take the exam and join the team. The ARRL Handbook is in my opinion THE source for information on radio science. I buy the book almost every year just to get the changes and updates. It's that good. I highly recommend it for readers in high school, college, and beyond.


zs6kmd (author)2015-07-11

Thanks for taking me on a walk down memory lane... I started with my first receiver 44 years ago and have never looked back. I note the comments regarding the kit era and have to admit that much of what has been said is true, but guys like us will always put something together to promote construction for others...

I know because that is what I do all the time, I have just put together a bunch of kits for Arduino for our local club as well as several other kits from receivers to transmitters and so on.

I like the design of this one so much that I just may make a PCB for it and share that with the scouts in the area for them to build...

Keep the ideas coming and well done on a great article...

73 ZS6KMD - South Africa

netzener (author)zs6kmd2015-07-11

Many thanks for your kind comment. I'm glad you liked the article. It is great to hear what you are working on because the SARL is actively promoting the radio sciences to young people, which is something you are doing as well. I don't think it is obvious to most people that global communications over the Internet depends heavily on a radio. The typical smartphone has three radios in it (GSM/CDMA, Bluetooth, and GPS). Modern laptop computers have at least two (WIFI, Bluetooth). If the Internet of Things ever actually becomes a thing, then that too will depend on a radio.

During my first year of college, I nearly drove myself crazy at the library trying to read and absorb everything about electrical engineering. When a professor of mine overheard what I was attempting he sat me down in his office and said, "Maybe in the 1800's and early 1900's you could go to college and learn everything that was then known about electronics. But today the field is far too deep and broad for anyone to comprehend it all. What you are attempting is impossible. There are 1000's of innovations and discoveries published every year. Even if you could read at 700 words per minute and only needed 4 hours of sleep a night, you couldn't keep up. I would recommend that you choose one discipline and concentrate on that".

He was right. But instead of one discipline, I chose two: Computers and Communications. Given how things have gone in the world of wireless, I'm very glad I made those two choices.

It sounds to me like you did that too and are actively teaching that to others. Good for you! Our civilization depends on how willing and thorough we runners are at passing the baton to the fresh athlete ahead.


JoeI2 (author)2015-06-28

I built a TennTech 2 meter transceiver once. I spent many hours on it and some traces came off the broad. The main board wouldn't match up with the control board, but I still felt I had done my best. I had planned to try again but as you say kits are gone. I like your Instructable, it shows what a lot of people giving instruction fail to, THE BOTTOM if I can't see how its put together I can't do it.

netzener (author)JoeI22015-06-28

I know what you mean. When I was a kid I tried to put together one of those visible V8 kits with the lights, sound, and motor... and failed miserably. More optimism than skill in my case. Not too long ago I decided I was going to give it another go, but Testors no longer manufactures the kit. Dang it! But I did have a great experience with the Haynes V8 model kit. That kit is really, really nice!

Many thanks for the feedback. My goal was to be as clear and complete as possible so that others could say "I made one of those". Good documentation, explanation, and illustration is essential. Before posting the article, I spent some time reading the comments and opinions of folks who like building kits or experimenting with electronics. The most frequent complaint I've seen could be paraphrased as "A lot of process but not a lot of theory". What many are asking for is a better explanation of what the parts do and why certain values were chosen:

"Why does this circuit work like that?"

"Why is this transistor specified instead of another?"

"What's the .01uF capacitor for?"

"How did you know that changing the 100 Ohm resistor to a 220 Ohm resistor would help that second transistor conduct better? I want to know how to do that."

I was seeking to explain how to build the radio and how it works without boring the reader with theory they perhaps were already aware of or weren't interested in. That's why I broke the article up into an Instructable (how it works and how to build it) and a blog post on my web site (the same thing with a lot more basic theory). I haven't quite hit the target accurately with this first project, but I hope to do so with my next project.

Thanks again for the feedback!


JoeI2 (author)netzener2015-07-02

What makes me unhappy is that about the time I was starting to find scrap electronics to salvage components from they went to surface mount with no markings, very confusing. Why did they stop marking components?

Build_it_Bob (author)2015-07-01

This was my favorite Radio Shack Pbox kit ! You did an amazing job with this "updated version". Time permitting I may just make your version this fall .

It looks just as much a showpiece as it is functional.

The trip down memory lane was a nice diversion from the day to day fast pace.

I also enjoy all the variations that analog and digital electronics offer. Arduino programming is my main interest these days. I enjoy Nuts and Volts magazine as well as Instructables to offer great ideas and tutorials.

Thanks as well to all that offered comments ; I found them very interesting to read through.


netzener (author)Build_it_Bob2015-07-01

Yes we seem to be a lively group over here. I enjoy the history of things technical and there are people on the site who were there when it happened and did a lot of it :-) I'm glad you enjoyed the article. If you need help with the radio, let me know.

When I was a teen my favorite thing to do in the fall was go to the bookstore and buy a couple electronics magazines off the shelf, get a burger and a coke, and sit out at the park and read. A family friend once gave me his entire collection of Electronics Illustrated magazines from 1968 through 1973. That's what got me hooked on the history of analog electronics. EI was one of the finest magazines around back then in my opinion. The covers were excellent and exciting, and the articles were well written. There was even a column about diagnosing and repairing TV sets that read a lot like a hospital drama. Pretty neat!

Thanks for the comment!


whitewolf499 (author)2015-07-01

Hi Guys,

I made one of these, or one like it, back in the 1980s and used the Tandy supplied tuner circuit board to wire into a normal AM receiver amplifier output stage. I fitted a slow motion drive to the tuning condenser. (OOPS, capacitor! Well, I AM 68 years young!) I boxed the lot and it is still here in my shack and working! raised a few eyebrows going through security in the airport though!!! Great circuit and keep 'em coming. I also work in valve/vacuum tube radios even to day. Very Best Regards from UK, Gary

WrshpMzshn (author)2015-06-24

Wonderful! Took me right back to 1970.

netzener (author)WrshpMzshn2015-06-24

Awesome! It was the golden age of electronics kits based on the catalogs I've seen. Heathkit was at their peak. Bell and Howell and DeVry worked together to create a correspondence school for learning electronics from home in your spare time. Many of the electronics training companies that popped up in the 50's to capitalize on returning military service people seeking job training were still operating. You could build a home stereo with all the advanced features for about half of the cost at a store. You could show your friends and say with pride, "I made that". Radio Shack was selling consumer electronics as hard as they could but still had lots of parts and kits on offer. So, yeah. It was a good time, the 70's. Fortunately we still have the Instructables community as an outlet for we "do-it-yourself" people.

eburman (author)netzener2015-06-28

Actually, I'm coming to believe that we are NOW in the Golden Age of electronics. Think all of the resources that we have now. Instructables, Make Magazine and the Maker movement, Adafruit, Sparkfun, easily obtainable parts via Digikey, Mouser, Jameco, Amazon, Ebay, Aliexpress etc., the amazing access to information that we now have via the internet and Google, an explosion of books on digital and analog electronics, access to micro controllers via Arduino, my gosh the list just goes on and on!

netzener (author)eburman2015-06-29

I certainly agree that it appears the Internet in the 21st century has had an impact a little like the printing press did in the 14th century with respect to the spread of ideas and making access to information more convenient. And I also agree that Velleman, Elenco, Canakit, Adafruit, and all the other folks you mentioned are thriving in the market they serve which is great for folks like you and me. I love it and wouldn't want to change it.

Here's where I am coming from on the "Golden Age" of kit building. Based on some study of vendors and products sold to electronics enthusiasts between about 1950 through 1979, the kit market was divided roughly into three categories: Consumer electronics, Education, and Experimenters. These three categories had (and still have) very distinct characteristics.

The Consumer Electronics kit market was composed of people with skills in soldering and assembly, and some electronics training ranging from industrial/military to college engineering. The builders primary goal was to obtain a device like a home stereo or a Ham radio in a cost effective way. The consumer electronics kit was complete with case, knobs, power supplies, power cords, operating manuals, accessories... everything that was needed for a complete home stereo, for example. The builder only needed to be willing do some part-time work in exchange for an affordable price. The builders secondary goal was pride in workmanship. They wanted to enjoy using a product they built themselves and show others the results of their hard work. Third priority was learning some electronics theory which wasn't actually done all that well by the vendors involved. Heathkit was the most successful company in this category and held the lead for decades. Due to rapid evolution of product features, shrinking part geometries, and declining prices for assembled/tested equipment the consumer kit market declined and no longer exists outside of some specialty and entertainment circuit kits (Velleman really excels here). I think that's a loss for the electronics enthusiast segment. I have no arguments with the commercial reasons for it's extinction. I just wish there were some kits that developed and challenged the craftsmanship of the builder. I think those skills are critical to learning how to create a well-designed product that others will cherish. Perhaps Instructables and Make are filling some of the gaps now, but Heathkit set a high standard of quality that is difficult to achieve.

In my view, the Training category has also declined but is still limping along. The biggest consumer complaint is "plenty of process but not enough explaining". I've reviewed manuals from the leading manufacturers in this category and the Heathkit and Bell&Howell/DeVry products did a really thorough job, but they are extinct. Almost everything available today is a kit of parts and a list of projects with not much in the way of theory and basic mathematics. A few simple and sometimes inaccurate explanations are about it. I can teach anyone to perform general analog/digital design with just a few equations per subject area. It really doesn't take much more than that. So I think there is a lot more that industry can do to make learning electronics more satisfying. LittleBits might be the closest to a kit that requires learning and mental problem solving.

Here's what I completely agree with you on: The Experimenter category has exploded! There are more quality options here than ever before. And this category continues to grow. The only complaint I have about the category is related to learning value with respect to electronics and physics. Many of the products on offer here aren't analogous to Lego building blocks. They are more like prefabricated Lego buildings. You can buy a quad-copter drone frame and motors already assembled, zip-tie 4 assembled motor controllers to the frame and wire them to a fully assembled flight controller, attach a battery and load some software. Bang! Quad-copter. Buy a Raspberry Pi, load the OS on a flash card, attach a WiFi and SDR module, plug it in and load some software. Pow! Software Defined Radio. Buy an Arduino Robot and add some software. Wham! Robot. See what I mean? I would love to see the players in this category help customers go a little deeper into the basics of control theory, radio theory, robotics, and physics so that their experiments can be more self-directed instead of downloaded.

Like you I'm glad electronics is still something people are curious about. As you can probably tell, I liked your comment too.



BeachsideHank (author)netzener2015-06-28

I took the Bell and Howell electronics technician correspondence course
using the G.I. bill while still in the navy, in 1972. The kits were
neat to build as instruction aids. Doing this on active duty used
very little of your bill's credits, so it was almost free, and was a
great way to pass off- duty time. It was still viable even while
deployed on a cruise, but then came our attachment to combat
operations on Yankee station in the south China sea, during the
Vietnam war. I was on a destroyer, and had precious little space to
call my own, but I made it work, in between general quarters, and
fire support missions, and surface actions (raids) up north, dog
tired but I kept it up, the only bright side was I could write “free”
in the envelope corner instead of paying to mail my lessons back as
you used to get franking privileges in a combat area. Unbelievably I
had the multimeter, and an oscilloscope for years before losing them
in a household move during the late '80's, but have fond memories of
that course and all I learned from it. Oh, by the way, my job on the
tin can was “boilerman”- a snipe, black gang, talk about trying
hard for upward mobility. When people complain about how hot it is I
smile inwardly, and think: unless you're standing in front of a 600
p.s.i. boiler roaring at flank speed with the superheater lit off in
the tropics during summertime while swapping fire with some very
capable gunners ashore, baby you don't really know what “hot” is!

netzener (author)BeachsideHank2015-06-28

It is a great honor to hear from a warrior. I've read some of the books and heard a few of the stories. A civilian like me won't fully understand the commitment, bravery, friendship, and sacrifice required in military service. It is unlike anything else in the world. Thanks for sharing your hard work on and off the line.