TUBE RECEIVER WITH EC92
(1973)

KLIK HIER VOOR DE NEDERLANDSE VERSIE


Student electronics.

No Radio officer
Radio officer on board of a ship, that was what I wanted to become. Two passions, Radio and the Sea in one profession. But there was no future in that profession. So I became a poor student electronics in an attic room. Classmates wanted motorcycles and even cars, but I did not need that! Freedom, happiness and simplicity, on free Wednesday afternoons barefoot to Amsterdam! To buy cheap books about radio! The Waterlooplein market! At that time, old radio equipment was still sold. I enjoyed it to see, but did not want to have it. However, buying a beautiful coil or special crystals that had to be possible! Very simple with toe slippers or bare feet, even in the snow! What a great simple and carefree life, no money, no belongings, no worries about mortgages and pensions! Only a few minor problems such as that sometimes a glass splinter had to be removed from my bare feet...


Barefoot to Amsterdam.
Then you had trains with real locomotives!

Some classmates were radio amateur. Friendly people who spend the whole day with talking about radio. They bought expensive two-meter transceivers and large, heavy shortwave receivers. But I wanted simplicity preferred to play with a crystal receiver. Listening to the shortwave broadcast stations during many hours was nice. Listening very simple to radio amateur with a simple regenerative receiver for 80 meters. With a tube, such as was used in the early days of radio! Indeed, I wanted to build such a receiver!
It had to be a receiver that easily would fit in a plastic bag to take it everywhere. There were still some parts and a EC92 tube left from experiments with illegal transmitters. It became a simple regenerative receiver with triode EC92 and a crystal phone. And with fine tuning. The control of the regenerationk was perfect. You could adjust it right on the edge of generation. Or slightly over it for optimum reception of weak SSB stations. And oscillating quite strong for strong SSB stations. The real historical radio sensation. A wire of 5 m along the rafters of my hired student room as an antenna. And the bed was used as ground.


The regenerative receiver for Scheveningen radio and 80 meter.
The zenerdiode is drawn, but never mounted.

Description
Unfortunately, there is no picture of the receiver. But I do have the original drawing of the diagram! It is a 0V0, so ony a detector tube, no RF and LF amplifiers.

Tuning
Between the antenna and receiver an additional tuned circuit was added to suppress the audio breakthrough of strong broadcast stations just above 4 MHz and strong broadcast stations on the 2nd harmonic, the 7 MHz broadcast band. For the reception of SSB and CW, the receiver has to oscillate. And the second harmonic of the oscillator signal fell exactly in the 7 MHz band. After this addition, the reception was free of interferences. The antenna is connected with the top of this tuned circuit via a capacitor.
Then follows the tuned circuit. Via a very small capacitor, the first tuned circuit is connected to this tuned circuit. There are two tuning capacitors, one for the coarse tuning and one with a parallel and series capacitor for the fine tuning. Because of the parallel and series capacitors, the influence on the tuning of this second capacitor is much less.

Detector
After the tuned circuit you can find the triode. It detects the RF signals by means of grid detection, the grid-cathode space works as a diode. For the regeneration, the cathode is connected to a tap of the coil. The regeneration is controlled by lowering of the anode voltage by means of a potentiometer of 500k. It works excellent but it seems to me not really a good method. As not only the RF gain is reduced, but also the LF gain. And you want to keep the LF gain as high as possible!
The capacitor of 470pF at the anode is the decoupling of the RF signals to ground. The next capacitor of 10nF provides the separation of the DC voltage and AC signal. The resistor of 47k and the capacitor of 2nF are a low pass filter. And the resistor of 100k prevents that there is a DC voltage over the crystal phone.

Supply
A single phase rectifier and elco is used. It is not drawn. The planned voltage stabilizer by means of the zenerdiode of 150 volt is not used. The 100k resistor and 0.1uF capacitor are used. And of course, the 6.3 volt filament voltage from the transformer is connected to the tube and at one side to ground.


The tube EC92
Variable mica capacitors were used for the tuning.

Crystal oscillator to tune the receiver.
Again barefoot to Amsterdam to buy crystals on the Waterlooplein market. One with a frequency of 2182kHz for the emergency and calling frequency for the shipping. And one with a frequency of 3640kHz to find the 80 meter band, the Oldtimer net. I made an oscillator, it did not need an antenna, as it radiated already enough. With a 9 volt battery, the connection clip was mede of an old 9 volt battery and was also the on- off switch.


The crystal oscillator used for tuning of the receiver.
Two frequencies, 2182 kHz for shipping and 3640 kHz for the amateurband (Oldtimer net).

And then the 0V0 was ready!
Radio does not have to be expensive! The control of the tuning and regeneration was working with hands and feet and never boring. Listening to Scheveningen radio for radio traffic with ships and radio amateurs. Of the Dutch radio amateur net, most stations could be received. That Duch radio amateur net is still there, Scheveningen radio not anymore... Listening to the Night owls net. Amateurs who talk with each other late at night.
Often a radio amateur in my neighbourhood thought that someone was tuning on the frequency. But of course, wat he did hear was my beautiful oscillating receiver! At that time I did not know what you can do with low power! This receiver was built in 1973. I still know that because all amateurs said "Best 73" to each other. I had expected that after the turn of the year it would become "Best 74"! How much fun you can have with such a simple receiver. Listening during many hours in the winter with my bare feet on the cold linoleum of my students room!


My very nice student room!
With real kitchen!


Later I did build a BFO in a real tube radio, left on the picture.

And radio officer?
I loved the sea! Walking on the beach from Zantvoort to IJmuiden. In the winter, because then the beach was so pleasantly deserted. There I stood with my bare feet in the cold water looking at huge ships that left the harbour and then I found it a pity that I could not become a radio officer anymore... Although,a radio operator wears polished shoes and certainly does not walk barefoot in Amsterdam of course! It might be that I was totally unsuitable for that job! That evening at home I listened to the ships with my 0V0. Not with polished shoes, but with my bare feet on the cold linoleum. And 25 years later the job of radio officer was History...


History!

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