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