Category Archives: Radio Modifications

Kostas pairs his Collins 51S-1 with a Heathkit SB-620 bandscope

Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following guest post which originally appeared on his radio website:


Collins 51S-1 band scope using a Heathkit SB-620

by Kostas (SV3ORA)

The purpose of this project, is to connect a Collins 51S-1 receiver with a Heathkit SB-620 “scanalyzer”, so as to give the 51S-1 band scope capability. Right into the schematic presented below, a slight modification is needed to the 51S-1. I usually do not do modifications to old equipment unless absolutely needed and even when I do so, I take care for them to be easily undone and to modify them as little as possible.

The modification to the 51S-1 is simply a small coupling capacitor connected to the plate of the mixer tube V4A and a short run of thin coaxial cable, connected as shown, to one of the several SPARE RCA connectors at the back of the 51S-1. Collins engineers were smart enough to include SPARE RCA connectors at the back of the radio, which are not connected to anything inside the radio circuit, to be used for different future purposes. So we do not have to drill any holes to the chassis of the precious receiver, which would be catastrophic.

 

Click to enlarge.

The coupling capacitor is just 5pF, so compared to C125, this presents only a tiny fraction of the loading to V4A plate, i.e. not affecting the normal operation of the receiver. Note, you cannot take directly the 500KHz IF output that is originally provided by the 51S-1 RCA in the back of the radio. This is because this IF is AFTER the filters, so it is a narrow IF. We need WIDE IF for the scanalizer to work properly, so you have to perform this tiny modification to the 51S-1.

No need to say that the SB-620 needs to be re-tuned for 500KHz instead of 455KHz. I was unlucky and my SB-620 did not have the appropriate L3 to be tuned to the IF of 455/500KHz. Mine had the L3 used for an IF of 5.2-6MHz. I converted the SB-620 to work down to 500KHz by using this original higher-frequency L3 and adding two additional inductors to it, one at its bottom and one at its top, so as to make L3 larger. The additional bottom inductor I added (connected from the bottom of L3 to the ground) was a 15uH choke. The additional top inductor I added (connected from the top of L3 to C3 and C5), was a 455KHz IF CAN transformer (the one with the adjustable yellow-painted cap) taken out of a transistor radio. Of course I have removed the internal capacitor of the transformer before using it. My transformer had something like 200-300uH in the mid-set point. It is not too critical as this is a tunable transformer.

By making this modification to the SB-620 you can bring the 5.2-6MHz L3, down to 500KHz. Of course the slug of L3 now has limited tuning range. But we can coarse tune the hybrid L3 now, by tuning the IF transformer that has been added. This solution worked like a charm and the original L3 is still fit in place, looking original and helps in fine tuning if needed. For the optional mixer input (points A, B, C on the SB-620), I used circuit #1, but I did not notice any real difference from circuit #3. RFC1 is 304uH and I connected three 100uH chokes in series to make this RFC.
The solution described in this page, will add a huge value to your vintage receiving station. SWLing feels just different by having an all-tubes computer-free band scope. Here is a picture of the setup, nicely glowing in the night. That P7 CRT blue phosphor with its green afterglow “memory” effect looks amazing! Narrow resolution is actually only achievable, because of this afterglow of the CRT, which allows for much slower sweep rates.

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Pavel fixes a stereo lock in the Eton E1

Many thanks to SWLing Post contributor, Pavel Kraus, who shares the following guest post:


Eton E1 – fault in stereo reception

I recently became the owner of an Eton E1 receiver, which I obtained on eBay from the USA.

The receiver is great, everything worked, error-free display. The only problem was that even FM and strong local stations did not play stereo even though stereo reception was set in the menu. The stereo text on the display flashed several times when the stations were not tuned in precisely, but after the stereo tuned, the text went out. I know that stereo reception is not the most important thing for this receiver, but it bothered me that there was a defect at all.

The Sanyo 3335 stereo decoder is used in this radio. The stereo reception switching threshold can be set with a 10kohm potentiometer which is connected to terminal 4 of the integrated circuit:

I disassembled the radio by loosening the screws on the back of the radio. The receiver is divided into two parts. I removed the XM module and disconnected the part of the radio with the display from the flat wires on the second printed circuit board of the radio

I then removed the screws on the circuit board located at the back of the radio.

I removed the printed circuit board and found a matching resistor trimmer on the other side of the circuit.

Then I connected these two points with a wire (when running on batteries) so that I could turn on the receiver:

After tuning in to a strong local transmitter, I carefully turned the trimmer until the stereo sign lit up and listening to the headphones made sure the sound matched the stereo. I repeated this at several local stations.

The receiver now plays stereo perfectly and the settings do not affect other parameters of the receiver. After assembling the radio, I was able to enjoy quality stereo reception.

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Guest Post: “Tinkering with History”

Many thanks to SWLing Post contributor, Bob Colegrove, who shares the following guest post:


Tinkering with History

By Bob Colegrove

One of the attractive aspects of radio as a hobby is that it has so many specialties to channel our time.  Just for the sake of classification, I would group these into two categories, listening and tinkering.  I think the meaning of each category is fairly intuitive.  Probably few of us approach our interest in radio in the same way.  Most of us have dabbled in more than one listening or tinkering specialty.  Perhaps we have been drawn to one particular area of interest, or we may have bounced around from one to another over a period of time.  I know the latter has been my case.

Tinkering might start with a simple curiosity about what makes the radio play, or hum, or buzz, and progress to an obsessive, compulsive disorder in making it play, hum or buzz better.  Unfortunately, over the past 30 years or so, the use of proprietary integrated circuits, as well as robotically-installed, surface-mounted components have greatly short-circuited what the average radio tinker can do.  For example, I have noticed a lot more interest in antennas over that period, and I think the reason is simple.  The antenna is one remaining area where a committed tinker can still cobble up a length of wire and supporting structure and draw some satisfaction.  But the complexity and lack of adequate documentation have largely kept newer radio cabinets intact and soldering irons cold.  Bill Halligan knew you were going to tinker with his radios, so he told you how they were put together.  The fun began when you took your radio out of warranty.  If you did get in over your head, there was usually somebody’s cousin not far away who could help you out.  The following is a sample of how one resolute tinker managed to overcome the problem of locked-down radios in the modern age. Continue reading

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Radio Mods: Unblocking the YAESU FRG-8800 Frequency Coverage Limitations

Many thanks to SWLing Post contributor, Paolo Viappiani (SWL I1-11437), who shares the following guest post. Note that, as with any radio modification, perform this operation at your own risk. This is a very simple mod, but if you feel it might be beyond your skill level, consider hiring a radio technician to perform it on your behalf:


Unblocking the YAESU FRG-8800 Frequency Coverage Limitations

by Paolo Viappiani

Figure I: An unblocked FRG-8800 receiver tuned to 29.999.9 MHz.

Introduction

It is well known that some receivers produced in the last decades of the last century suffered from a limited frequency coverage due to legislative restrictions in force in some countries (Germany, Australia, etc.).

In particular, in Germany it was forbidden to listen to HF frequencies higher than 26.1 MHz, while in other Countries shortwave were not allowed to receive frequencies below 2 MHz.
These restrictions led most radio manufacturers to produce “blocked” versions of their HF receivers in order to satisfy the various national requirements; almost classical examples are the world renowned SONY ICF-2001D and the PHILIPS D-2935/D-2999 portables.

The blocking/unblocking procedure of some frequency bands was quite simple in microprocessor-governed synthesized radios: usually it was sufficient to add (or remove) proper jumpers in the vicinity of the microprocessor to perform the task, and the correct procedure was often covered in the Service Manuals or in specific Technical Bulletins; in any case plenty of information can be found on the Internet. Continue reading

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Jerome makes an aluminum back stand for the PL-880

Many thanks to SWLing Post contributor, Jerome van der Linden, who writes:

Hello Thomas,
I have managed to break three of these flimsy PL-880 back stands, and thought, “how hard can it be to make one out of metal?”

These two photos are the result from a piece of aluminium that I had in the shed (yes I know you guys call it aluminum) . Here’s hoping it lasts longer!

I love it, Jerome.  I’m willing to bet your backs tand will outlast the PL-880 now!

Thanks for sharing. I love this simple aluminium (remember, I lived in Europe–ha ha) solution! 🙂

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Radio Waves: Radio and Education, Border Blasters, FM Switch Delayed per DCMS, and A Quick Temporary AM Antenna

Radio Waves:  Stories Making Waves in the World of Radio

Because I keep my ear to the waves, as well as receive many tips from others who do the same, I find myself privy to radio-related stories that might interest SWLing Post readers.  To that end: Welcome to the SWLing Post’s Radio Waves, a collection of links to interesting stories making waves in the world of radio. Enjoy!


Can Radio Really Educate? (JSTOR Daily)

In the 1920s, radio was an exciting new mass medium. It was known for providing entertainment, but educators wondered if it could also be used for education.

It was mid-1922 and America was in the midst of the radio craze. Commercial broadcasting had emerged in a handful of cities in 1920, but at that time, few people had a receiving set—except for amateur radio operators, who knew how to build one. It wasn’t even called “radio” back then—newspapers referred to it as “radiophone” or “wireless telephone.” But only two years later, there were several hundred radio stations on the air, and you could purchase a radio in a store—although hobbyists still had fun trying to build their own, with varying degrees of success. Meanwhile, the word “radio” had become the common term for that wonderful new invention that everyone wanted in their home.

Today, we tend to take radio for granted; it is one of many ways to hear music or news or sports. But in 1922, radio was unique: it was the first mass medium to take people to an event in real time, and listeners were amazed by it. Suddenly, they could hear a popular orchestra coming through the radio set. Without leaving their home, they could listen to a baseball game, or an inspirational talk from a preacher; some stations even had the latest news headlines. In an era when traveling from one city to another could take hours (the popular Model T Ford had a top speed of 40-45 mph, and superhighways had not yet come along), listeners could travel by radio, hearing stations from distant cities. Before radio, only the wealthy could attend a concert featuring a famous vocalist, but now, anyone who had a receiving set could hear that singer’s music. And in an America that was still racially segregated, radio gave some musicians of color the opportunity to be heard by thousands of listeners. In magazines and newspapers, radio inspired “utopian hopes and bold predictions.” Writers referred to it as a cure for loneliness—especially for people living in rural areas or on the farm. It was also praised for helping the blind gain greater access to the world around them. More than one writer claimed radio would bring world peace, since everyone would unite around their favorite programs. And of course, as a sign of American progress, it was something no home should be without, not even the White House: President Harding was an enthusiastic radio fan, and had a set installed near his desk, so he could listen whenever he wanted to. [Continue reading…]

Psychics once ruled the airwaves thanks to the Texas-Mexico border and the magic of radio (KUT)

A new book includes details of how powerful radio stations along the border helped former vaudeville actors reach larger audiences.

In the 1920s and ’30s, some of the most popular radio programs in the United States featured radio psychics. The most successful among them made hundreds of thousands of dollars reading the minds and predicting the futures of eager listeners. To do it, they took advantage of a new and mysterious medium: radio. Continue reading

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Gary DeBock’s XHDATA D-808 loopstick model

Many thanks to SWLing Post contributor, Gary DeBock, who shares the following:

The 7.5 inch (19cm) loopstick XHDATA D-808 model was designed to be the ultimate AM-DXing (or Longwave DXing) travel portable, and can be built for a construction cost of around $30 US. It has already been used by numerous DXers to track down transcontinental and transoceanic AM-DX during overseas travel, and the orange plastic loopstick frame allows full operation of the whip antenna for FM and Shortwave reception.

The modification procedure isn’t difficult, and the full construction article is posted at

https://dreamcrafts.app.box.com/s/5d0pi85jfptgmrj4pd0jsmaybgb6gteh

A video demonstration of its daytime DX performance (compared to the stock model) has been posted on YouTube:

Build one, and join the fun! 🙂

Many thanks for sharing this, Gary! Your ultralight DXing creations are simply amazing!

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