The EK4ACI Hartley
EK4ACI, Prof. Schmitz, was one of the twelve first legal individual licenses in Germany. Schmitz is also known as the legendary "MARS" He was one of Germans Radio pioneers. A few pictures of his early setups survived. Prof. Dr. Karl Lickfeld, DL3FM, found out that his mentor Schmitz was one of Germans radio godfathers and tried to make some researches about Prof. Schmitz as a radio amateur. The pictures of his setups show, that some parts were used in all his station arrangements (canibalizing of earlier setups), so it is possible to see the development of his transmitters. One picture has written a text on the backside, informing that it shows the last version of the station setup, so Lickfeld put this picture chronically at the end of the row, and regarded it as an amplifier. But he was not sure about the function of some details. I got Lickfelds research results on a CD, available from Heinz Sarrasch, DJ7RC. When I saw this picture, I recognized immediatelly that it must be a self-oscillating Hartley transmitter, and not a linear. The variable "Hartley point" showed that clearly. Further, it is a very simple setup, so I am pretty sure that it shows one of EK4ACI's first transmitters, possibly his very first. The text wants to tell this is the final version of THIS transmitter, and not the very last setup. It is not fair to discuss the statements of someone who can't defend his own arguments: DL3FM is silent key. I decided to "prove" my interpretion and built this Hartley transmitter. Instead of 2x RS5 tubes I had to use a "211", a tube introduced 1929 and still under production nowadays! Thanks to Don, VE3LYX from the AWA reflector for this hint! A pair of German RS5 is unavailable today! The parameters of a single 211 are pretty the same compared to 2x RS5. I tried to stay very close to the arrangement of the original. My first setup used very nice variable capacitors from the 20'ies, but I had arcing in the isolation bushings. So I had to replace this vintage variable capacitors by a bit more modern versions.
Since January 2018 I am QRV with that replica, mainly on 80m. I get 10-12W output with a surprisingly good tone. The tube is capable to deliver much more, but the trick with self oscillation is to run everything very conservatively in order to get a good tone and stable conditions.
Today I think that the transmitter visible on the original picture shows a setup from the early 20'ies. In issue 2/1927 of the "Radio World", "4ACI" was listed with an asteric, what meant that he was heard in North America using AM modulation! This can never have taken place with the transmitter seen in the picture! There os no provision made for modulating the signal.
Here is the picture of the original (Thanks to Heiz Sarrasch, DJ7RC, for his permission to publish it!)
If you like the picture, I recommend to buy the CD from Heinz with a lot of highly interesting, additional infos about EK4ACI.
Here some comments (sorry, in German only) about the parts:
And this is the replica with 1x 211 tube, picture taken with the 80m coil.:
Power supply running at 700V. For 12W out the current reads about 35 mA.
Output matching: A swiveling flat "pancake" coil. The cross is not made of wood, it is phenolic material. The meter shows the "Luftdrahtstrom", the current in the antenna wire.
The resonance coil (here for 80m) with the clip for the adjustable "Hartley point" creating the feedback for self-oscillation. In Germany, a Hartley was called "Dreipunkt-Schaltung".
So see you on the air with this transmitter. But please be patiant with my signals! You will hear every raindrop running down the ladderline, and every gust waving my antenna in the wind will create some howling of the signal. These transmitters are full of life. Using them makes you experience the behaviour of RF circuits more then every DDS setup can ever do! I am not an Electronic Man, so I can tell you that I have learned a lot when building all this historic equipment you see on my homepage.
And no, these radios are not good for "599" QSOs....;-)