Most industrial radios converted into transceivers have low output power when transmitting. As a rule, the generated RF voltage does not exceed 1 - 1.5V at a load of 50 ... 75 ohms. In my home radio station, together with a converted R-399A radio receiver, a simple power amplifier is used on two widely used GU-29 lamps. Schematic diagram of the amplifier is shown in Fig.1.

Specifications amplifier:

• Input impedance .................................. 75(50) ohm;
• The amplitude of the input RF signal .................... 1 ... 1.5V;
• Anode current................................................... ..... 400 - 450 mA;
• Output power at a load of 75 ohms ........ 150 W

Fig.1.

The quiescent current of the lamps is set automatically by two D815D zener diodes connected in series and for two GU-29 lamps is 70-80 mA. The design of the power amplifier has no distinctive features. It is assembled in a metal case 300 x 300 x 80 mm. The lamps are placed horizontally.

Transformer T1 is wound on a cylindrical frame with a 600 NN ferrite core. A frame from the IF circuit of the Alpinnst-403 radio receiver may come up. The design of the anode and anti-parameter choke, as well as the data of the P-loop, can be found in the reference literature.

Setting

The amplifier is easy to manufacture and tincture. In the transmission mode, a voltage of -15V is applied to the KT920B transistor, the quiescent current of the transistor (without signal) is 120 mA. Within a small range, it can be set by selecting the resistor R3. Transformer T1 is shunted with a 2 kΩ resistor. For more stable operation of the amplifier, it can be selected.

V. Milchenko, (RZ3ZA)

Comments on the article:

UM on two GU29

V.Milchenko RZ3ZA

The amplifier is assembled on two parallel-connected lamps GU-29. The amplitude of the input signal is 1 ... 1.5 volts. Anode current-400...450 mA. Output power at a load of 75 ohms-150 watts.

In the transmission mode, the KT920B transistor is supplied with a voltage of -15 volts, a quiescent current, and a quiescent current of the transistor (without signal) -120 mA. Within a small range, it can be adjusted by selecting the resistor R3. Transformer T1 is shunted with a 2k resistor. The quiescent current of the lamps is set automatically by two D815D zener diodes connected in series and for two lamps is 70-80 mA. The lamps are located in a housing 300x300x80 mm horizontally. The T1 transformer is wound on a cylindrical frame with a 600НН ferrite core.

Literature: magazine "Radioamateur" No. 8 1997

UM on two lamps 6P45S

Hybrid PA with transformerless power supply

E. Golubev, RV3UB

PA with transformerless PSU and protection

For example, a PA circuit with a power supply protected from phase reversal with zero is shown. The entire article can be read: Radio magazine 1969 No. 3 p. 19

CATEGORY 1 RADIO POWER CONTROL

Literature: "Radio" 1979 No. 11 G. Ivanov (U0AFX)

Transformerless power supply in the UM

PA for MW radio

This power amplifier is designed to operate a portable radio station in stationary mode. In this case, the signal from its output is fed to the input of the amplifier through a coaxial cable. The power of a portable radio station with an input impedance of 50 ohms of a power amplifier is 1-2W. This power amplifier develops power up to 30-40W. The output is designed for a 75-ohm antenna.

The amplifier circuit is shown in the figure.

The signal from the output of the transmitter goes to the input X2 to the input of the double lamp VL1 GU-29, the signal goes to the control grids of this lamp. R7 brings the input impedance of the amplifier to 50 ohms. The anode load of the lamp is the choke L2, from which the signal enters the U-shaped filter L1 C3 C4 and then goes to the antenna. The output stage of the transmitter is equipped with an SWR meter that allows you to measure both direct and reflected SWR. This makes it possible to adjust the output circuit using capacitors C3 C4.

The power source is transformer, it contains 2 rectifiers and three parametric stabilizers.

L1 is wound with copper wire (bare) with a diameter of 2 mm, without a frame, winding diameter 25 mm, winding length 22 mm, number of turns 8. L2 is wound on a frame with a diameter of 20 mm and contains 150 turns of PELSHO 0.25, winding length 80 mm. L3 L4 are wound on resistors R2 R4, they contain 5 turns of PEV 1.0 each. L5 L6 - throttles DM-0.5. T1 - 6 turns of PEV 0.31 with a tap from the middle wound on inner core coaxial cable, which goes from L1 to the output connector (the shielding braid is removed at the winding point).

T2 is wound on a magnetic circuit Ш25 * 32, winding 1 -1030 turns of PEV 0.25, 2-1300 PEV 0.25, 3-60 turns of PEV 1.0 with a tap from the middle, winding 4 contains 175 turns of PEV 0.2.

Amplifier mounted in metal case bulk installation. If necessary, it is necessary to carry out heat dissipation using a fan to blow the lamp.

R8 sets the lamp quiescent current within 15-17mA. the alternating control voltage supplied to the grids of the lamp (U on R7) should be about 10V and not exceed 15V.

Amplifier on lamps 6P42S

The difficulty of obtaining average power levels (about 100 W) in transistorized silos forces us to look for other solutions. It can also be the same as suggested by Muscovite V. Krylov (RV3AW). He created a push-pull amplifier with two 6P42S lamps operating at a supply voltage of only 300 V. The output power of the amplifier is 130 W with an input power of about 5 W.

The push-pull switching on of the lamps makes it possible to significantly (up to 20 dB) reduce the radiation at the second harmonic compared to a conventional amplifier. A broadband transformer T1 with a transformation ratio of 4 is installed in the anode circuit of the lamps. As a result, the amplitude of the RF voltage at the output P-circuit is halved and it becomes possible to use a standard KPI from a broadcasting receiver. Simplicity of the device and accessibility element base allow us to recommend this power amplifier for repetition. The scheme is shown in fig.

Coil L2 is made on a plastic ring (size K64x60x30) with MGTF wire with a core cross section of 0.5 mm. The taps are made from 2, 4, 8, 12 and 20 turns. Transformer T1 is made on a magnetic circuit of two rings with a size of K40x25x25 from ferrite 2000NN. The windings contain 12 turns of MGTF wire with a core cross section of 0.5 mm. The T2 transformer is made on two ferrite (2000НН) rings folded together with a size of K16x8x6. Each winding consists of 8 turns of MGTF wire with a core cross section of 0.15 mm2. Winding T1 and T2 was carried out simultaneously with three wires.

Transformerless RA on GU-29

I.Avgustovsky (RV3LE)

 The idea of ​​building a push-pull amplifier based on electronic tubes is not new, and the circuitry of this amplifier, in principle, is no different from the circuitry of building push-pull transistor amplifiers. It should be noted that current lamps work best in this circuit, i.e. lamps with low internal resistance, which are capable of providing a significant anode current pulse at low supply voltage. These are lamps of type 6P42S, 6P44S and 6P45S. However, I managed to build an amplifier with good characteristics even on a GU-29 lamp.

The range of amplified frequencies is 3.5 ... 29.7 MHz.

The power supplied to the anode circuit is 150 watts.

Efficiency - 65%.

Output power at the antenna equivalent 75 Ohm in the ranges:

o 3.5 ... 21 MHz - 100 W;

o 24 MHz - 90 W;

o 28 MHz - 75 W.

Power consumed from the network at rated voltage in the network and the maximum output power - 200 watts.

Dimensions:

o width - 160 mm;

o height - 150 mm;

o depth - 215 mm.

Weight - no more than 2 kg.

A distinctive feature of this amplifier is its transformerless power supply circuit. The advantages of such a power supply scheme are obvious - with an input power of 150 W, taking into account the efficiency of the power supply, a power transformer with an overall power of at least 200 W is required. In this case, the dimensions and weight of the power supply itself are comparable to the parameters of the power amplifier itself and far exceed the dimensions and weight of an amplifier with an input power of 500 W on 6P45S lamps.

I made this amplifier as an experimental one back in 1994, but from the very first day of operation it proved to be so good that it still works without any alterations. During this time, more than 10,000 QSOs have been made on it. All correspondents invariably note the excellent signal quality. Despite the fact that my antennas are only 2 ... 3 meters from the collective television antennas, TVI are completely absent.

I also want to note that the GU-29 lamp in this design is operated in a very hard mode (power input - 150 W), but despite this, for two and a half years of operation, I did not find any deterioration in power characteristics. Consider the circuit diagram (Fig. 1).

 The input signal is applied to the primary winding of a broadband transformer based on the T1 line. The non-inductive resistor R1 is the active load of the power amplifier of the transceiver itself and allows you to get a linear frequency response of the latter.

The amplified anti-phase signal from the anodes of the lamp is fed to the T2 transformer, to the midpoint primary winding which the anode voltage is applied. The amplifier load is switched on through a conventional P-circuit, the signal to which is taken from the secondary winding of the T2 transformer.

The amplifier is powered through a rectifier assembled according to the voltage doubling circuit on diodes VD1, VD2 and capacitors C10, C11 (Fig. 2).

 Screen grid voltage (+225 V) is stabilized. The bias voltage is obtained from a separate rectifier VD5, C9 from the secondary winding of the incandescent transformer T3.

Pay special attention to the fact that none of the sources feeding the amplifier (~6.3V, 0, -Ucm, +225V, +600V) is connected to the chassis! The amplifier chassis is used as a common wire only at high frequency.

Parts and designs of the amplifier

Since the galvanic isolation of the power supply circuits from the chassis is carried out through transformers T1 and T2, special attention should be paid to the thoroughness of their manufacture. The T1 transformer is wound on a M30VCh brand ferrite ring with an outer diameter of 16 mm (20 mm is possible). First, sharp edges are removed from the ring with fine sandpaper. Then the ring is wrapped with at least three layers of PTFE tape. The winding of the transformer is carried out simultaneously with three wires in fluoroplastic insulation MGTF-0.12 without twisting. The number of turns is 12.

The T2 transformer is similar in design to the T1, but is made on two M30VCh rings folded together with an outer diameter of 32 mm (36 mm is possible). The windings of the T2 transformer also contain 3x12 turns of MGTF-0.14 wire without twisting. The ends of the windings are fixed with threads. Polyethylene film should not be used as insulation due to its non-heat resistance.

I do not give the parameters of the P-circuit, they are easy to calculate using the available methods. In the author's version, the L3 coil is wound on a fluoroplastic ring with an outer diameter of 70 mm and a cross section of 15x15 mm2 with a silver-plated wire with a diameter of 1.5 mm and with its taps rests on a ceramic biscuit of the SA1.2 range switch. Capacitor C5 is a tuning capacitor with an air dielectric of the KPV-150 type. C8 - standard two-section PBC 2x12 ... 495 pF from broadcast receivers.

All blocking capacitors C1 ... C4, C12 ... C14 are of the KSO type for a voltage of at least 500 V or similar with a rating of 0.01 ... 0.1 μF.

In the power supply (Fig. 2), the diodes VD1 and VD2 are KD226G or KD203A, which allow a large current pulse, which is inevitable at the moment the power is turned on, since this design does not have a large inductance in the form of a power transformer. The charge current of capacitors C10 and C11 reaches tens of amperes within a few milliseconds, therefore, a resistor R6 is installed to protect the diodes VD1 and VD2 from breakdown. Its value is not critical and can range from 330 ohms to 1 kOhm. A few seconds after the amplifier is turned on, it is short-circuited by the SA3 "Anode" toggle switch. Resistors R7 and R8 serve to equalize the voltage across capacitors C10 and C11.

Transistor VT1 and zener diodes VD3 and VD4 are mounted on small heatsinks isolated from the chassis. Trimmer resistor R9 - any type, but with good insulation. Incandescent transformer - with an overall power of at least 20 W and with well-insulated windings.

Anticipating the question of readers about possible replacements for ferrite rings for transformers T1 and T2, I want to say the following: rings with a permeability of 30 VCh can be replaced without damage by any of the indicated sizes with a permeability of 20 VCh ... 50 VCh. I have not experimented with rings with a permeability of 100 NM...600 NM, and rings with a permeability of 1000 NM...3000 NM will obviously not work here.

The power supply and the amplifier lamp have galvanic contact with the network, so care should be taken during the setup process. Once again, I draw your attention: the "0V" circuit should not have contact with the chassis! The input (before T1) and output (after T2) amplifier circuits are absolutely safe and must be connected to the chassis according to the diagram.

Linear Power Amplifier for SSB/CW/AM

With an input power of 200 W, the output power is 120 ... 130 W. The amplifier operates on two GU-50 pentodes according to the scheme with three grounded gridsThe input impedance of the amplifier is 50 ... 70 Ohm, which allows you to connect it to the exciter with a piece of coaxial cable with the same impedance.

To achieve a current of 200 mA at an anode voltage of 1200 V, an excitation power of 7...10 W is required. The quiescent current is a few milliamps. Peak power (input) can be increased by amplifying single-sideband signals up to 400 watts without endangering the lamps, since the average input power will be about 200 watts. Inductor Dr1 with an inductance of about 300 ... 500 μH must be designed for a current of 200 ... 250 mA

Power amplifier for SDR - 1000

This power amplifier is designed for joint work with a software-defined transceiver SDR-1000, the output power of which is about 0.5 W, although the output power is declared to be at least one watt. In addition, it can be used in conjunction with any type of transceiver radio receiver, for example, R-326M, R-399A, R-160P.

The power amplifier consists of two stages: a broadband voltage amplifier, made on transistors VT1 and VT2, operating in class A - driver, and the power amplifier itself, which uses two GU-29 lamps connected in parallel and operating in class AV1.

This amplifier has been designed and manufactured for everyday on-air applications where its power output is more than sufficient. GU-29 lamps were used due to their fairly good linearity and availability. The amplifier has output power about 100 watts on all ranges. The input voltage is 3 Volts, due to the use of an attenuator made on resistors R15..R17, which attenuates the input signal by 14 dB (5 times the voltage). If a output voltage, which must be applied to the input of the amplifier less than 3 volts, then you can install an attenuator with less attenuation, or even abandon it altogether. The sensitivity of the cascode voltage amplifier on transistors VT1 and VT2 (driver) is quite high and equals 0.5 V. The dimensions of the case are 137 x 240 x 240 mm, which was determined as available.

In the power amplification stage, a circuit with a common cathode and excitation voltage was applied to the grid. When the RA is operating, the input signal through the RF connector XW1 and the contacts of the relay K1.1, the attenuator, enters the input of the U-shaped low-pass filter (LPF), the cutoff frequency of which is 47 MHz. LPF - C11, L6, C13, plus the input capacitance of the transistor VT2 has a Butterworth characteristic, with a blockage of the amplitude-frequency characteristic at a cutoff frequency of 3 dB. The use of LPF is useful for several reasons at once. The first is a decrease in the level of higher harmonics, the second: the low-pass filter compensates for the input capacitance of the transistor VT2, as a result of which the input resistance PA becomes frequency-independent, and the amplitude of the excitation signal does not fall with increasing frequency. Without LPF on the upper ranges, it would fall by more than 35 ... 45%. In addition, the low-pass filter helps to get a good standing wave ratio (SWR) at the input of the power amplifier. As a result, the transceiver operates on a matched load. As you can see, the use of LPF is more than justified. The output of the low-pass filter is loaded by the input impedance of the driver, which is reduced to 50 ohms. From the load resistance of the driver R14, the amplified high-frequency voltage is supplied to the control grids of the lamps VL1 and VL2 .. The gain of each lamp is 50 / 14 = 3.57 times in voltage, or 12.75 times in power, which is 11.1 dB. This is certainly not much, but more is not required. The task of filtering side oscillations at the input of the amplifier was not set, since the output circuits of the transceiver cope with this. Although, some filtering of higher harmonics is certainly present. In this case, two lamps connected in parallel work for a common load, P - circuit.

Relays K3 and K4, closing to the case at both ends in the transmission mode, a piece of coaxial cable serving for "Bypass" increase the stability of the power amplifier.

Throttle 4 and capacitor C17 serve to protect the power supply from possible VHF oscillations during self-excitation of the RA. At the output of the P-circuit, for ease of adjustment, a high-frequency voltmeter is installed. In transmission mode, when the pedal is depressed, electronic key, made on the transistor VT2, see Fig. 2, comes into action, the transistor VT2 opens and the relay K1 ... K5, included in its collector circuit, is triggered. The contacts of the relay K5.1, in Figure 2, are switched, and the screen grids of the lamps are supplied with supply voltage from a voltage regulator made on the VT1 transistor, which, despite its simplicity, showed good results. Resistor R6, which is connected to the output of the stabilizer, increases the stability of the voltage regulator in receive mode. The operation of the stabilizer can be further improved by using a light bulb for the appropriate voltage and current instead of the ballast resistor R4, and which will play the role of a barter, improving the stabilization coefficient.

The power transformer Tr.1 of the power supply is connected to the network smoothly, through a current-limiting resistor R1, which is then short-circuited by the contacts of the toggle switch B1 having an average neutral position. This simple circuit inclusion significantly extends the life of the lamp and power transformers, and the entire RA as a whole. It is known that the filament of a cold lamp has a resistance several times less than the filament of a heated lamp. Therefore, the starting current of the lamp filament is several times higher than the rated filament current of the lamp. Such a high turn-on current overloads the filament, destroys its structure, and reduces the life of the lamp. Therefore, the use of soft start is more than justified. The anode power supply has protection against anode current excess. Resistor R11 in Fig. 1 limits the current during a breakdown or short circuit of the output of the anode voltage source at a level equal to 535 / 10 = 53.5 A. The applied diodes of the FR207 type will withstand this current pulse and will not fail. The anode power source is made according to the doubling scheme and has fairly good dynamic characteristics, which is ensured by the sufficiently large capacitances of the electrolytic capacitors used in the circuit.

All parts related to the high-frequency unit are interconnected by 20 mm wide bars, which are cut from tinned tin from instant coffee cans. Connected to the busbars: lamp cathodes, variable capacitor current circuits included in the P - circuit, antenna connector, ground terminal, blocking capacitors in the anode choke circuit. Particular care should be taken to connect the KPI current collectors (capacitors of variable capacity), the grounded terminals of additional capacitors connected to them, and the cathodes of the lamps to the bus. Between the grounding points of the KPI and the cathodes of the lamps, there should not be any grounding of other parts going to the case, since a large loop current flows between them.

The input capacitances of the low-pass filter (C11, C13) are composed of two capacitors of the KT-2 type, you can use one capacitor of the KT-2 type, the value of which is selected using instruments.

Dr.1 contains 7 turns wound on a mandrel with a diameter of 10 mm with a high-resistance wire made of nichrome with a diameter of 0.8 mm. Throttle length 25 mm, outlet from the middle.

Dr.4 contains 5 turns wound with PEV-2 wire 1.3 mm on a mandrel with a diameter of 10 mm, winding length 18 mm. The inductance coil L6 of the LPF input filter contains 8 turns of PEV-2 1.2 wire. Winding frameless, diameter 8 mm? Winding length 14.5 mm. The low-pass filter, attenuator, driver are enclosed in one common screen located near the radio tube panels under the chassis.

The anode KPI was taken from some industrial equipment.

Loop coil data is shown below. Taps are counted from the hot end (anode) everywhere.

Coil L4 has 9 turns of frameless winding, diameter is 30 mm, winding length is 32 mm, wound with silver-plated wire with a diameter of 3 mm, tap from the 3rd and 6th turns..

Coil L5 is wound on a frame with a diameter of 40 mm. Contains 25 turns, wire diameter is 1.2 mm, winding length is 40 mm. Branches from the 6th and 13th turns.

The anode choke is wound on a fluoroplastic rod with a diameter of 18 mm, the length of the winding is 90 mm, the wire is 0.4 mm, the tap from the middle.

Relay K1, K3 and K4 type RES-49, passport RS4.569.421-00. Relay K2 - type REN-33, passport RF45 100021-0002, Power transformer Tr1 used type TS-180.

The cathodes of the VL1 and VL2 lamps fit to point a, where they are connected to the zener diodes VD1 and VD2, which create a bias voltage with two separate pieces of the mounting wire: ab and ac. This is necessary, otherwise self-excitation cannot be eliminated. Resistors R6 ... R10 also serve to suppress self-excitation of the power amplifier.

The power amplifier operates in class AB1. The quiescent current of the lamps, equal to 100 ... 120 mA, is obtained automatically, you just need to select the zener diodes in the cathode circuit so that they have a positive voltage of the order of 18 ... 20 V relative to the chassis.

The input low-pass filter must be adjusted, if necessary, on the 28 MHz band, focusing on the minimum SWR in the cable connecting the transceiver to the RA. The setting is made by selecting the inductance L6 and the input capacitances of the LPF. In addition, the "Antennoscope" from K. Rothammel is very well suited for this purpose, plus any generator high frequency, for example, G4-18A. The SWR value in this case is found as the ratio of resistances. Setting up the driver is quite simple and comes down to setting the quiescent current of transistors VT1 and VT2 of the order of 80 ... 90 mA by selecting resistors R11 and R13.

P - the circuit should first be set up in a "cold" way, the scheme of the stand is shown in Fig.3. It should not, as recommended by some authors, disconnect the lamps and the anode choke from the circuit and replace them with an equivalent capacitance. Firstly, it is difficult to accurately measure these capacitances, and not everyone has a capacitance meter, and secondly, the anode choke in the parallel power circuit is connected exactly in parallel to the P-loop coils (using blocking capacitors C17 and C18). Consequently, a loop, reactive current flows through it, depending on the quantities AC voltage on the anode of the lamp and the inductance of the inductor itself. As is known, at parallel connection two or more self-induction coils, their total, total inductance value decreases and becomes less than the value of any of the parallel-connected coils. It is clear that the greatest decrease in the size of the self-induction coil of the P-loop will occur in the range of 1.8 MHz. In the range of 28 MHz, the influence of the anode choke on the decrease in the inductance of the loop coil is insignificant, is within the error of the measuring instruments, and can be neglected. When manufacturing coils exactly as described, tuning comes down to checking for resonance in the middle of the ranges. For this, a heterodyne resonance indicator (GIR) is suitable, which, despite its simplicity, is a universal high-frequency device and is completely undeservedly forgotten in our time. Do not forget about the neon light bulb, which, when mounted on a long fiberglass shelf, is an excellent peak indicator of high-frequency voltage and allows you to accurately determine the moment of fine tuning the P-circuit to resonance, or, for example, the presence of self-excitation. By the color of its glow, one can approximately determine the frequency of self-excitation: at the operating frequency, the glow of a neon bulb has a yellowish-violet color, and when self-excited on VHF, its glow takes on a bluish tint.

The anode current of the lamps with a detuned P - circuit should be about 300 mA. The anode current of the lamps with a configured P-circuit should not be less than 240 ... 250 mA. That is, the "dip" of the anode current during the adjustment of the P-circuit should not exceed 60 mA, since in this case the anode current is redistributed "in favor" of the current of the screen grids of the lamps. Therefore, a larger current of the screen grids will cause their power overload , and the lamps will go into an overvoltage mode, which is undesirable, since the linearity of the RA will deteriorate.

A well-tuned power amplifier does not interfere with television and other household equipment. It is quite possible to use GU-19 lamps, which are slightly more linear and less prone to self-excitation.

Literature:
1. Cascode broadband power amplifier. Radio #3, 1978
2. L. Evteeva. "Cold" tuning of the P-loop of the transmitter. Radio, 1981, No. 10.

Alexander Kuzmenko (RV4LK).