Evan's AM Transmitter Circuits
Use of these circuits is subject to the laws of your
country of residence.
On this page I will detail my efforts to build a high quality tube-type AM transmitter. If you step through each page carefully, you'll come to see my own learning curve. This may save you some time! I will include lots pictures so you can see the evolution.
As for myself, I hold an FCC Radio/Telephone license and I'm a Certified Electronic Technician. However, I am not a radio engineer and I will not pretend to be one. My details will not give you the scientific information and measurements that many other website's will offer. However, I've spent a lot of time working to improve each design and you just might benefit from this. If your able to improve a circuit please feel free to share your findings with me.
For many years I've restored old radio's. However with less and less quality AM radio content being available, several years ago the idea came to me to build an AM transmitter. So I ordered the AM transmitter kit sold by Antique Electronic Supply. It worked as described, however I was never very happy with it. The quality of the broadcast made it challenging to listen to Old Time Radio Broadcasts. The spoken word was not clear and distinct. Additionally, oscillator tubes need to be driven by an audio source that is 1v to 2v peak-to-peak. This is more than most computers, or iPod's are able to produce. They are typically limited to 1v peak-to-peak at best. To mitigate this I built a solid state daughter-board to increase the audio to an acceptable level. (Schematic shown on the Three Tube TX page.)
Now, I would have really liked to give a big "thank you!" to Fred Nachbaur. Though Fred is no longer living, I really appreciate his kindness in making his AM transmitter circuits available to all of us.
http://www.dogstar.dantimax.dk/tubestuf/amtx.htm (Now offline)
However, Fred's AM transmitters can be seen here:
You will see pieces from his different AM schematic/s forming the basis for my latest transmitter/s, I've built them into new and somewhat different transmitter/s... look carefully you'll see many subtle changes. This includes the "Goldberg" design, which has been updated. After months of building and testing, I believe the audio quality of the "Goldberg" original only got better due to these revisions.
Additionally, I would like to thank several different individuals from Antique Radio Forums. (http://www.antiqueradios.com) Tom, Bill, Norm, Dennis, wa2ise, Justin, Bob Weaver.... and no doubt a few others.
I've studied various transmitter schematics from these individuals and attempted to build the best transmitter I can, using a pentagrid oscillator. I've gleaned several useful tips from these prints and incorporated a few of these into my transmitter and schematic diagrams. My goal in hosting this web page is to present realistic schematic/s, so you can build your own transmitter, simply by gathering the parts, assembling and adjusting the unit. I must say, this can be an amazingly satisfying bit of fun.
The Best-Quality transmitters are the "Goldberg", and now the two "Power" transmitters. The "Goldberg" uses a 6v compliment of tubes. At the heart of this transmitter is the dual input 12AT7 audio amplifier and the 6GY6 oscillator 7 pin tube. The two "Power" transmitters depart from the earlier pentagrid oscillator design. They are controlled carrier transmitters which helps prevent over-modulation and under-modulation. The 6GH8A is at the heart of this design. Both "Power" transmitters are somewhat simpler to build, are more linear and are really fantastic to listen to.
Listen to one transmitter with the 6GY6 tube, as heard on the little portable radio shown below, I recorded the audio with my iPhone sitting in front of it, to listen simply click the radio picture below:
With any AM transmitter, buzz and hum can be a real issue. You'll see, by looking at the various schematics, that I've taken steps to minimize this problem. If all else fails, switch off the circuit feeding your ground-fault circuits in your house. This can be a real source of RF noise generation. Lastly, change the crystal frequency to a higher value such the one shown here: http://www.xminusone.com/am/goldberg/Goldberg-Modified.jpg
Please feel free to e-mail me if you have questions or comments. Don't hesitate to give me advice on ways to improve anything you see. However, please do not send me offensive, thoughtless e-mail's. I would never do that to you. :-)
At this site:
Based on the Antique Electronic Supplies kit
Now it's crystal controlled.
a selectable preamp, solid state or tube.
A -revisit- with new circuit updates!
Linear 'power' Transmitter!
A simple performer!