Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The UM-3 power amplifier from R-105 (R-108, R-109) military radio stations can also be used for amateur radio purposes. Its output power is about 50W and it is very reliable in operation. However, for practical operation of CW, SSB, FM, RTTY and SSTVb as part of an amateur radio station, the amplifier requires some modernization. The author of the article used the modernized UM-3 when working on the amateur bands from 10 to 20 m, both with the R-108M radio station and with a transceiver of his own design.

One of the advantages of the UM-3 is the ability to match its output with almost any antenna. The amplifier circuit is shown in fig. 1.

Rice. 1 (click to enlarge)

The amplifier consists of a preamplifier on a 6P15P lamp, an output stage on a GU-50 lamp, an antenna matching unit and a mode measurement unit. Its performance can be improved with minimal modifications.

Food

To power the UM-3 amplifier, you can use a standard BP-150 converter, powered by a 12 V battery. This is convenient when you have a car battery at hand. However, it must be remembered that with the full output power of the amplifier, a rather large current is consumed from the battery - 12 A. When working on the air from home every day, it is more rational to use a home-made AC power supply. Its scheme can be any, and we will leave it to the choice of the reader. The current requirements for the power supply are as follows: in the +800 V circuit - at least 200 mA, in the +280 V circuit - at least 150 mA, in the +12 V circuit - at least 4 A, in the -100 V circuit - about 5 mA .

If you cannot find a counterpart to the KhRZ connector, through which the UM-3 is connected to the power supply, then you can replace it with any other one that is suitable in terms of overall dimensions, for example, the 19-pin 2RMD27KPN19G. The pinout of the KhRZ connector and possible replacement of the counterpart is shown in the table.

Contact 4 of the standard connector when switching the relay (transition from reception to transmission) is connected to the body and can be used as a switching confirmation signal.

Switching

When using UM-3 in normal mode (BP-150 and R-105), there will be no problems. But when operating in conjunction with other radios, you must use only pin 1 of the XP4 connector "K PR." To transfer the UM-3 to the transmission mode, it must be connected to the body.

For normal amplification of SSB signals and in order to avoid self-excitation of the amplifier when working with them, you need to change the lamp modes by supplying -42 V instead of -100 V to their control grids. The easiest way to do this is to add an additional power circuit (Fig. 2) by installing a divider from a tuned resistor FT with a resistance of about 50 kOhm in a -100 V circuit (pin 2 of the KhRS connector) and a blocking capacitor C of the KSO type with a capacity of 1000 pF.

The setting comes down to setting the resistor P / quiescent current, measured in the +800 V circuit (pin 6 of the KhRS connector). Before starting the adjustment, the slider of the resistor R' must be set to the upper position according to the diagram. For CW and FM, the quiescent current should be about 5 mA, for SSB about 25 mA. Linearity is not affected. At a quiescent current of more than 25 mA, UM-3 becomes prone to self-excitation.

Resistor R' is most conveniently placed next to the GU-50 lamp and the power connector, and capacitor C is next to the 6P15P lamp and relay K1, located next to the right wall of the amplifier. It is necessary that the wires of the added circuit are as far as possible from the anode circuits of the lamps.

For quick switching of modes when operating with different types of radiation (CW, SSB), it is recommended to assemble an additional switching circuit, shown in Fig. 3. Resistor R "- with a resistance of 5 kOhm. Relay K' can be used with any nominal winding voltage of 12 V. When the relay contacts are closed (CW mode), the resistor is short-circuited and a larger bias will be applied to the lamp control grids than in the SSB signal amplification mode .

The UM-3 amplifier can also be used outside the standard frequency range. Its tuning to the 20-meter band (it is possible to other bands, but it was not performed in the author's version) is extremely simple. To do this, you need to install only two additional capacitors of constant capacitance: the first one with a capacitance of 120 pF, in parallel with the variable capacitor C10 of the grid circuit of the GU-50 lamp (its axis is displayed on the front panel under the appropriate name), and the second with a capacitance of 75 pF in parallel with the capacitor C6 (such the same KPI, only in the lower section) of the anode circuit of the same lamp. It is best to use capacitors of the KD type for a voltage of at least 2 kV.

In conclusion, I would like to note that despite the existence of various modifications of the amplifier, only very old models have minor circuit differences (for example, the 12xxx series does not provide for the operation of a radio station with the PA turned off), and these improvements are valid in all existing models.

The use of relay K' can be abandoned by replacing it with a toggle switch, but if the location of the new wires is unsuccessful, the amplifier may self-excite.

Author: A.Babushkin (RK3DOV), Kolomna, Moscow Region

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