While most of my ham activity has centered around building and using high power gear for DXing, I have always felt an odd fascination for “antique” radio, especially ham rigs from the 1920s era. Many times through the years I have come across pictures of these old beauties in books, magazines, or on the web. Invariably my heart skipped a beat, my eyes glazed over (so I’m told), and I started to think how much fun it would be to build something like that. How can you not love the wonder and simplicity of the era, the magic of it all? A primitive tube and handful of components mounted on a board, and voila… you have a transmitter! Not much different for the receiver.
Somehow I always managed to close the book or shut off the computer and run like heck before temptation got the better of me. Until, in early 2011, my long time friend and EME mentor Ron, N4GJV, told me people were not only still building 1920s ham gear, but using it on the air! What?! In particular Ron mentioned the Bruce Kelly event held in December each year. The object is to fire up rigs representing 1929 or earlier technology and make QSOs. Ron mentioned VE7SL’s TNT Transmitter page as a good place to see some of these extraordinary rigs. There I found not only pictures of many rigs, but Steve’s construction notes and – perhaps most intoxicating of all – links to other sites, some of which led me to videos and audio recordings of “1929” rig signals. There was no getting off the hook now! I knew I had to build one of these rigs!
I decided of all the designs I looked at, I was most interested in building what is known as a TNT transmitter, short for tuned plate, not tuned grid. Like most simple (affordable) transmitters of the era, the TNT is a self excited oscillator. These rely on a simple L/C tuned circuit to set the frequency of operation. From all that I read one has to be careful about every detail if a good sounding signal is to be had. The power supply should be well filtered and have minimal voltage sag with keying; the transmitter needs to have good components, rigidly mounted to avoid movement, and the transmitter should be isolated from any environmental vibration; and it must be tuned very carefully. Sounds like a fun challenge!
I also wanted to build a 1929-appropriate receiver to use with the transmitter. Being on a tight budget I wanted something simple but not too simple. After some thought I decided on a design using two tubes: a UX-201A regenerative detector and a UX-201A audio amplifier.