Encyclopedia of radio electronics and electrical engineering / radio reception
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A large abundance of various designs of tube receivers currently makes it so difficult for a beginner radio amateur that he often does not know what to take on, which circuit to choose, which receiver to build.
This description is intended to assist the radio amateur in finding a scheme that gives good results. The lamp receiver brought to the attention of readers is the result of lengthy experiments. The principle of the described receiver, with some changes and additions, is known under the name "Filadina".
The described tube receiver, subject to its careful assembly and the presence of a good antenna, allows the reception of many allied and foreign radio stations on the telephone, and some even on a loudspeaker, for an audience of 10-15 people. Reception of a local station and very powerful distant ones is possible on a frame, lighting network and other antenna surrogates.
Circuit feature
The schematic diagram is shown in fig. one.
Fig. 1
As can be seen from the diagram, here the three-electrode lamp is used in a very peculiar way. The oscillatory circuit of the receiver, consisting of a coil L1 and a capacitor of variable capacitance C1 (which tunes in to incoming waves, is not connected between the grid and the filament, as is done in almost all conventional circuits, but in series into the filament circuit of the lamp. Thus, the incoming electromagnetic oscillations are supplied to anode and lamp filament.The coil L2 is also included in the filament circuit, which serves to carry out regeneration.A high positive voltage of 30-40 volts is given to the grid of the lamp.
The grid circuit also includes: feedback coil L3 and telephone T. To obtain the most favorable operating mode of the circuit, it is necessary to select such an anode voltage at which the voltage change between the filament and the anode causes the greatest changes in the grid current. To achieve this, a small positive voltage of about 5-6 volts is applied to the anode, adjusted by means of a potentiometer P included in the high voltage part of the battery. Blocking capacitors C2 and C3 of the order of 800-1000 cm (900 ... 1100 pF (1 centimeter \u1,11d 1 (XNUMX) pF)) serve to create a more convenient path for high-frequency oscillations. Detection in the lamp occurs due to the fact that its characteristic with this inclusion is highly asymmetric.
A feature of the described circuit is that the lamp here operates at a very high positive voltage on the grid, which eliminates the space charge, instead of the harmful effect that the space charge has on the amplifying capabilities of the lamp and its output power. The lamp switched on according to this scheme has a high gain, and therefore the described receiver gives a greater effect than a conventional regenerator.
Installation
The practical implementation of the receiver is not much different from a conventional regenerator.
The number of turns of coils L1 and L2 depends on the received range. Feedback coil L3 should have 20% fewer turns than coil L2. It should be especially noted that the link variable between L2 and L3 is absolutely not required. This eliminates the need to install a reel machine. When choosing the type of coils L1, L2 and L3, it is best to focus on honeycomb coils. The change in the degree of regeneration in this circuit is achieved by changing the lamp mode and can be very easily regulated by changing the anode voltage using the potentiometer P. When constructing this receiver, it must be remembered that the direct filament current passes through the coils L1 and L2, so they should be wound from a sufficiently thick wire, in any case, not thinner than 0,5 mm.
Details
In conclusion, it is necessary to indicate the total number and data of the details of the receiver.
1) Variable capacitor C, with max. with a capacity of 500 cm550 (XNUMX pF). Desirable for smoother tuning and adjustment with a vernier.
2) Antenna coil L1 replaceable, cellular and 35-75 turns.
3) Coils L2 and L3 are also cellular, replaceable.
4) Potentiometer P must be bought ready-made. Its resistance is 500 ohms.
5) Capacitors of constant capacity C2 and C3 of the order of 800-1000 cm (900 ... 1100 pF).
6) Heating rheostat - R with a resistance of 26-30 ohms.
Author: A.Kodash
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