Posted By: Robert Nickels (W9RAN) Posted: 11/312/2023 Heat up the iron 0 Comments 11/312/2023 |
KA8WQL's "Trifecta Receiver" |
In racing, a trifecta is "a run of three wins or grand events." When I read the first sentence of Bob KA8WQLs article about his homebrew receiver, the word trifecta came to mind because he managed to do all three things at the same time! I think you'll agree!I read once, a long time ago, that the Radio Amateur should have three stations: one that looks good, one he built himself, and one that actually works. While I’m sure this was meant in jest, I have tried to incorporate all of these attributes into my station. Like many hams, I enjoy building my own equipment. The creation of something useful out of a bunch of old parts has proven to be an enjoyable and rewarding pastime. A fully home-built station has always been a goal of mine, not simply for economic reasons but also for the wealth of knowledge and enjoyment gained from such a pursuit. I got my Novice ticket as a high school kid in the 1980’s. Most of my exposure to Amateur Radio came from old 1960’s QST magazines that I would get from the local used bookstore. They were filled with construction articles and often featured fully home-built stations. In the February 1966 issue of QST, Lew McCoy, W1ICP, had a nice simple transmitter project in the Beginner and Novice column. It was a one-tube 6GW8 design called the “Mighty Midget” that became my first transmitter. Decades later my involvement with vintage AM operating had caused the vacuum tube bug to bite again, and since I spend most of my radio time listening, I decided to build myself a vintage HF receiver to use with my Heathkit DX-60A. This receiver was constructed with a great fondness for vintage vacuum tube receivers and the spirit of homebrew electronics that was popular in their time. I used only junk-box parts and tried to keep all hardware appropriate to the era, such as using all slotted screws and no semiconductor devices.
While thinking about receiver designs, I remembered that Lew McCoy’s little transmitter was followed-up a few months later with a companion receiver project, the “Mate for the Mighty Midget” (QST, April 1966). This receiver was a simple superhet with an interesting bandswitching arrangement that did not require switching in the RF and mixer stages. His transmitter had worked, and served me well as a Novice, so I dug out my old musty ’66 QST. It was a good place to start, even though I would eventually change much of it.
The receiver I eventually built is a 3-band, 9-tube single-conversion superhet. The RF and mixer stages are continuously tunable from 3.5 to 7.3 MHz via a front panel preselector control as in the original W1ICP design. Only the local oscillator has to be switched to change bands. This tuning scheme greatly simplified construction and meant that I could add any band of frequencies between 80 and 40 meters by adding another oscillator. My first thought was to add 60 meters, but this would require switching the BFO for upper sideband. I didn’t want the extra work, especially since the receiver was likely to be used mostly on AM and CW anyway. So I added the 49 meter shortwave band (5850 to 6200 kHz), which is still quite active. The RF amplifier was changed to a 6BZ6 circuit as used by Hammarlund in their HQ-170/180 models. Input and output transformer coils were hand-wound with #26 enameled magnet wire on 7/8-inch bakelite forms. The main tuning capacitor is a Hammarlund MC-100 with several of the rotor and stator plates removed to obtain the proper bandspread. The oscillator tank coils were wound on ¼-inch forms with powdered-iron slugs. These can be adjusted via holes in the bottom cover for frequency calibration. A 6EA8 is used as the mixer/oscillator, with the pentode section as the mixer and the triode section the oscillator.
The original design was for a 455 kHz IF and single-pole crystal filter. I didn’t have any of the required crystals, so I needed to figure something out. Fortunately, my junk box had some old crystals from a Heathkit HR-10 parts unit. That meant that I had to switch to a 1682 kHz IF. A little math showed that this would work without image problems and, better yet, was the IF frequency used in a lot of old Heathkit receivers of that era, including an old GR-54 I had on the junk pile. This was the source of the IF and BFO transformers. I managed to have the proper crystals to make a switchable single-pole IF filter, with 2.4 kHz normal and 700 Hz narrow bandwidths. The IF amplifiers are a pair of 6BA6’s, with circuit values pretty much straight from the GR-54 schematic. AM detection is a classic 6AL5 diode, while CW/SSB uses a 12AT7 twin triode product detector and fixed-frequency BFO. Audio-derived AGC is applied to the RF and IF amplifiers and is also used for the S-meter. Muting is achieved in the normal manner, opening the cathode circuits of the RF and IF amplifiers. The audio and power supply circuits are pretty standard, using a 6HF8 as an AF preamp/amplifier. Even without feedback, the audio amplifier seems stable with plenty of gain. AM reception sounds great using an old 6x9 speaker.
As you can see, there’s nothing new or innovative in any of this. All of these are time-tested circuits used in many commercial vacuum tube receivers. The tricky part is getting them to work together and getting the gain distribution right, and a bit of time was spent with a resistance substitution box to that end. The result is a surprisingly stable receiver that can easily hold its own against my Heathkit HR-10 or Hammarlund HQ-110. With the product detector and crystal filter, it even outperforms them on CW and SSB. Not quite top-of-the-line, but not bad either.
As I do with many of my projects, I created a Technical Manual which includes detailed circuit descriptions as well as alignment instructions and all diagrams. I think this is important – I’ve seen a lot of nice homebrew gear at swap meets, but without documentation it’s difficult to know what it actually does or how to connect it. Even including a schematic diagram inside the case of simpler projects can be useful to future users, or often to myself if I have to service it.
The receiver has been in use now for a bit over ten years. I currently use it with both my DX-60A and my newly-restored DX-100B. Listening to all my friends on a radio that I built myself is a real thrill, especially when that radio glows in the dark. And as it turns out, it looks good, I built it myself, and it actually works!
-Robert Majkrzak, KA8WQL
|
On the workbench
Posted: 08/226/2024
Comments: 0 |
Making SMT "no lead" parts easier to use
... READ MORE |
Monitoring Post
Posted: 04/93/2024
Comments: 0 |
Skyking Skyking do not answer. Message follows...
Anyone who caught one of the Emergency Action Notifications (EAN) transmitted by the US Air Force on the HF bands remembers this phrase.But not many know how the EAN is actually used by our military. This re-creation of a Minuteman III Launch Control Facilitliy (LCF) in Utah provides a realistic view of what happens when an EAN is received by a missile control crew, 60 feet under... READ MORE |
On the workbench
Posted: 01/22/2024
Comments: 0 |
Grind your own?
If you're a long-time ham you might know what the smeary figure-8 pattern is....Back in the Novice era, many used crystals purchased from suppliers like JAN Crystals who purchased large quantities of military surplus crystals and reground them for the ham bands. That's why they were cheap, but also why you couldn't get a specific frequency as they'd grind by a formula and is long... READ MORE |
Heat up the iron
Posted: 12/364/2023
Comments: 0 |
K5HZ's "AC-2" Compactron transmitter
Ron K5HZ has been building equipment since he first got his ham license in the early 60s, and while he has other transmitters, all it took to build a new one was finding a "free to good home" power transformer at a hamfest. It also gave him a chance to try using a couple of Compactron tubes that had caught his eye - the 6T10 dual pentode and the 6GE5 beam power pentode that was d... READ MORE |
Brass Pounding
Posted: 12/341/2023
Comments: 0 |
DigiKeyer
If you build almost anything electronic, chances are good you've purchased parts from DigiKey Electronics. But did you know that DigiKey - now one of the world's largest electronics distributors - started out as a ham radio company?"More than 50 years ago, a digital electronic device designed to generate uniform Morse characters and spaces was made available for sale by amateur radio enthusi... READ MORE |
Looking Back
Posted: 11/332/2023
Comments: 0 |
Heathkit - An Employee Looks Back
Electronic Design magazine published an excellent interview in 2020 with Chas Gilmore W8IAI, former Heath engineer, manager, and executive. Anyone with an interest in Heathkits will find this interview to be well worth the time to read. You can read it for free without registration here at the ELECTRONIC DESIGN WEBSITEThe photo below was borrowed from W8IAI's QRZ page, and shows h... READ MORE |
On the workbench
Posted: 11/320/2023
Comments: 0 |
Fusing the DX-40
Upon examining a DX-40 given to me by a good friend, I was surprised not to find the usual fused plug on the AC line cord. I thought maybe Heathkit realized the error of their ways and had put one inside - but no. A check of the schematic confirmed that fuses were never a part of the DX-40 design. This needed to be corrected but after first considering hogging a... READ MORE |
Heat up the iron
Posted: 11/312/2023
Comments: 0 |
KA8WQL's "Trifecta Receiver"
In racing, a trifecta is "a run of three wins or grand events." When I read the first sentence of Bob KA8WQLs article about his homebrew receiver, the word trifecta came to mind because he managed to do all three things at the same time! I think you'll agree!I read once, a long time ago, that the Radio Amateur should have three stations: one that looks good, one... READ MORE |
Tech Library
Posted: 11/311/2023
Comments: 0 |
EIA Codes - a clue to "who made what"
Although Source Codes ceased with the 2001 edition, it is available here for historical purposes.The EIA Source Code is a numeric symbol that was assigned and registered by the Electronic Industries Association (EIA) that could be stamped or marked on any or all products to identify the production source or the vendor assuming product responsibility.In addition, the EIA code provided for adding nu... READ MORE |
Tech Library
Posted: 10/302/2023
Comments: 0 |
David Gleason is an unsung hero
While working as a Univision programming and research exec in the early 2000, David Gleason began digitizing publications about the radio and TV business and posting them on his personal website so that he could easily share them as he traveled around and met with station staff.It was helpful in persuading the locals to take his advice, he says. “Rather than it just sounding like my opinion,... READ MORE |
Looking Back
Posted: 10/276/2023
Comments: 0 |
John Wells, Cliff Harvey, and the Harvey-Wells Electronics Company
Through the courtesy of the author, Hamilton K. Agnew, it's a pleasure to share this history of one of ham radios pioneering companies - Harvey Wells Electronics. The company was a very important contributor to world-wide electronics, both during WWII and many years after, as well as a substantial manufacturer of ham radio equipment.Download it from the link at the ... READ MORE |
Tech Library
Posted: 08/234/2023
Comments: 0 |
Ballast Tube data and substitutions
Here's some information that isn't often needed, but difficult to find: A. P. Jacobi's Ballast Tube Handbook and Substitution Guide. Download from the "Attachments" link below.... READ MORE |
Tech Library
Posted: 08/214/2023
Comments: 0 |
Electricity Explained
We've heard there is some confusion about how electricity works. This should clear things up.... READ MORE |
Brass Pounding
Posted: 06/172/2023
Comments: 0 |
A Poem about Morse Code
A member of the Long Island CW Group thought he'd give one of those AI chatbot sites a challenge...he didn't expect much but got a real surprise... In a world of signals, hidden and grand,A language of dots and dashes, hand in hand.Morse code whispers, in rhythm and sound,A symphony of messages, profound. With a simple click, a dot appears,A fleeting moment, to the listening ears.Short a... READ MORE |
Looking Back
Posted: 06/171/2023
Comments: 0 |
The History of the Car Radio
Seems like cars have always had radios, but they didn't. Here's the story:One evening, in 1929, two young men named William Lear and Elmer Wavering drove their girlfriends to a lookout point high above the Mississippi River town of Quincy, Illinois, to watch the sunset. It was a romantic night to be sure, but one of the women observed that it would be even nicer if they could listen to music in th... READ MORE |
Looking Back
Posted: 06/171/2023
Comments: 0 |
History of the Car Radio
Seems like cars have always had radios, but they didn't. Here's the story: One evening, in 1929, two young men named William Lear and Elmer Wavering drove their girlfriends to a lookout point high above the Mississippi River town of Quincy, Illinois, to watch the sunset. It was a romantic night to be sure, but one of... READ MORE |
Tech Library
Posted: 05/125/2023
Comments: 0 |
DIY Layout Creator
If you're like most homebrewers, often times you just want to build a one-time-only circuit and end up with a haphazard layout or one you have to tear apart and start over on to get everything to fit. DIY Layout Creator is designed for just this purpose! Not only do you get a layout that will work but a document that shows what you did so when you come back to it 3 weeks la... READ MORE |
Tech Library
Posted: 04/105/2023
Comments: 0 |
Minimalist QRP Book by IZ3AYQ
Everyone probably remembers building - or at least thinking about building - a small simple transmitter or receiver from an article in one of the radio magazines. They may not have used the term "minimalist" back then but the idea was the same - no frills, just a simple rig that could be easily assembled and was capable of being used on the air. Nowadays, QRP operati... READ MORE |
Monitoring Post
Posted: 04/91/2023
Comments: 0 |
The NEW WBCQ - 9330 kHz - Last Chance Radio superstation
Everyone who listens to shortwave is familiar with WBCQ, Monticello Maine USA aka "the Planet" and it's owner Allan Weiner who has been a legit broadcaster for many years after a youthful flirtation with pirate radio. But if you think WBCQ is a rag-tag collection of old SW transmitters held together by baling wire attached by Timtron - you are WAY out of calibration! &... READ MORE |
Welcome to the Shack
Posted: 03/89/2023
Comments: 0 |
Mr. Harvey Wells, Kelley W8GFG (SK)
Long-time particpants in the Midwest Classic Radio Net will remember Kelley W8GFG, who was always looking for "anything Harvey Wells". We lost Kelley too young in 2011 but his persistent quest from St. John IN is an abiding memory. I remember meeting him at a Chicago area hamfest and asking if he had any spare Harvey Wells speakers. He said no, they were very ra... READ MORE |