Gk 71 characteristics of a circuit with a common cathode.
V. Fedorchenko, rz3tl, Dzerzhinsk.--------
The power amplifier is made using a GK71 lamp - time-tested, reliable, with graphite anodes, which does not require forced cooling. The amplifier circuit is classic, with a common grid. Anode voltage - 3 kV, screen grid - 50 V, filament voltage - 22 V (in sleep mode - 11 V), quiescent current - 60 mA. With an excitation power of 50-80 W, the amplifier provides an output power of 500-600 W at a 50-ohm load.
Features of the amplifier circuit include protection against overcurrent and short circuit, as well as "sleep" mode. For better coordination with imported transceivers, a resonant circuit is used in the input part of the amplifier, and to achieve constant output power on all ranges, an original P-circuit circuit is used.
The amplifier is powered by one powerful power transformer made on a toroidal core. A high anode voltage (2.5-3.0 kV) is obtained after rectifying and doubling the voltage removed from the step-up winding of the power transformer.
When the amplifier is turned on, the 220 V mains voltage passes through the S43-Dr5-S44 network filter, the circuit breaker sf 1 and is fed to the primary winding of the power transformer through a halogen lamp vl 3, which ensures “soft” switching on of the amplifier, extending the life of the GK71 lamp and other circuit elements. After chargingcapacitors are part of the high voltage taken from the divider r 8-r 13 and potentiometer r 14, fed to the automation circuit on a transistor vt 3. If there is no short circuit in the high voltage circuit and the voltage is normal, then the transistor vt 3 opens, relay K4 is activated, closing the lamp with its contacts vl 3 and ensuring the supply of full alternating voltage to the primary winding of the transformer.
A feature of this automation circuit is the low hysteresis of the operation and release of relay K4, which provides reliable protection of the amplifier from various overloads - anode current, short circuits in secondary circuits, breakdown and short circuit in the windings of the power transformer. If these faults occur, the transistor vt 3 closes, relay K4 is de-energized, and the network winding of the power transformer is connected to the AC network through the lamp vl 3, which prevents failure of the amplifier elements.
In standby mode, the GK-71 lamp is supplied with partial filament voltage (11 V). This ensures low heating of the lamp and amplifier as a whole, i.e. "sleep mode". When switching to the transmission mode (TX), the full filament voltage (22 V) is applied to the GK71 cathode, and after 0.2-0.25 s the amplifier is ready to operate at full power. This is the undoubted advantage of direct filament lamps GK71, GU 13, GU81 and others.
To more fully match the amplifier with imported transceivers, a “cathode” circuit is used, tuned to resonance in the ranges of 7-28 MHz. When operating in the 28 MHz range, the circuit is formed by a coil l 3, made of a copper tube (its design is described below), and capacitor C22, and to obtain resonance in the lower frequency ranges of 7-24 MHz, capacitors C11-C16 are connected to this circuit.
In the low frequency ranges of 1.8 and 3.5 MHz, the “cathode” circuit is quite narrow-band, therefore, to more fully match the transceiver with the amplifier, instead of the circuit, a wideband transformer T1 is used, to which input signal supplied through relay contacts K9. At the same time, to eliminate HF influence, the coil l 3 “short-circuited” through capacitor C17 and through contacts K11.1.
On all bands, the SWR at the amplifier input does not exceed 1.5, which ensures excellent (or) matching of the amplifier with any imported transceiver, even one that does not have a built-in antenna tuner.
The output P-circuit of the amplifier is switched by a three-bar switch: sa 4.1 switches coil taps l 2 and connects additional capacitors C6 and C9 to the “antenna” KPI in the ranges of 1.8 and 3.5 MHz, sa 4.2 shorts the coil l 1 1.8 MHz band (or 3.5 MHz if the 1.8 MHz band is not used), sa 4.3 connects range relays K8-K13, through the contacts of which capacitors C11-C16 and auxiliary relays KB and K7 are connected to the “cathode” circuit.
When operating in the 28 MHz band, a coil is used l 4, which is installed directly in the anode circuit of the GK71 lamp. This implementation of the P-circuit made it possible to obtain an output power of at least 500 W in this range (as in the low frequency ranges!). Choke Dr1 is necessary to protect the output circuits of the amplifier.
Reception/transmission control(rx/tx) implements a transistor circuit vt 1, which is powered by a voltage of +24 V. When the “TX” input is closed to the common wire (the current in this circuit is 3-5 mA), the transistor opens vt 1 , relays K1 (switching the input RF circuits of the amplifier), K2 (switching the output circuits of the amplifier) and K5 (supplying full filament voltage to the GK71 cathode) are activated. If the switch sa 2 is installed in the lower (according to the diagram) position, then the full filament voltage is supplied to the GK71 lamp constantly, which is sometimes necessary when working in competitions.
After charging capacitor C45 (after 0.15-0.2 s), the short-circuit relay is activated and its contacts K3.1 closes the circuit of the first lamp grid vl 1 to the common wire. The lamp opens and goes into amplification mode. This circuit design ensures correct operation of the amplifier and the absence of burning of relay contacts K1 and K2.
To ease the thermal conditions of the amplifier, a computer fan (12 V/0.15 A) is installed, which mainly operates at a reduced voltage (7-8 V), providing silent airflow. The fan control circuit is made using a transistor vt 4. When the amplifier switches to transmission mode through an open transistor vt 1 and resistor r 39 capacitor C49 begins to charge. After 4-5 s the transistor opens vt 4, and the fan starts working at higher speeds, because a voltage of about 12 V is supplied to it, which is set by selecting the resistance of the resistors r 41 and r 42 and depends on the type of fan. After switching to the receive mode, thanks to the slow discharge of capacitor C49, the enhanced airflow is maintained for another 40-50 s, providing intensive cooling of the amplifier.
When switching on for short periods of time in transmission mode, the fan operates at a reduced supply voltage, without creating unnecessary acoustic noise. If another fan is used, then it is possible in the collector circuit vt 4 install a 24-volt relay, the contacts of which will switch the fan operating mode.
In Bypass mode using the switch sa 1 the supply voltage is removed from the circuit on the transistor vt 1 , which prevents the amplifier from switching to transmit mode when a control signal arrives at the “TX” connector.
On transistor vt 2 An adjustable screen grid voltage stabilizer is made. Using a variable resistor r 18 set the quiescent current of the lamp vl 1 within 50-60 mA.
+24 V voltage source based on an integrated stabilizer da 1 used to power relays and automation circuits. In case of overloads and a short circuit in the +24 V circuit, the integrated stabilizer automatically turns off, which increases the reliability of the amplifier as a whole.
The amplifier uses a power transformer made from hardware from a 9-amp LATR. Iron dimensions - 130x75x75mm. The primary (network) winding contains 230 turns of 01.5 mm wire, but if the PA is used in everyday use and not in competition mode, then you can leave the “native” primary winding of the LATR. The step-up winding should contain 1200 turns of wire 00.65-0.7 mm (alternating voltage - 1.1-1.2 kV), the incandescent winding - 11+11 turns of wire 01.5 mm (voltage - 11+11 V ), the remaining windings are -14+35 turns of wire 00.5-0.65 mm (voltage - 22 and 50 V).
The broadband transformer T1 is wound with a wire of 01.2-1.5 mm in two wires on a ferrite ring K45x27x15 mm with a permeability of 2000NN and contains 12 turns, the communication coil - 7 turns of MGTF-0.2 wire, evenly distributed between the turns of the main winding.
Coil l 1 wound on a frame 040-45 mm and contains 15+12 turns of wire 01.5-2.0 mm. The first 15 turns are wound turn to turn (for the 1.8 MHz range), and the remaining 12 are wound with a pitch of 2.5 mm.
Coil l 2 wound with a copper tube 04-5 mm and contains 15-17 turns, outer diameter - 50-55 mm.
Coil l 3 cathode" circuit is made of a copper tube with a diameter of 4-5 mm, inside which a wire in heat-resistant insulation (MGTF, BPVL, etc.) with a cross-section of at least 0.7 mm 2 is stretched. The outer diameter of the coil is 27-30 mm, the gap between turns - 0.3 mm, number of turns - 8, tap - from the middle.
Coil l 4 made of copper winding wire 02.0-2.5 mm and contains 5-6 turns, the outer diameter of the coil is 25 mm.
Choke Dr1 (Universal winding) is wound with 00.2-0.3 mm wire and consists of 2-4 sections of 80-100 turns each; anode choke Dr2 - with PELSHO-0.35 wire on a fluoroplastic frame with a diameter of 18-20 mm and a length of 180 mm. Winding - turn to turn, in sections of 41, 34, 32, 29, 27, 20, 17 and 11 turns, and the last 10 turns - unevenly, in increments of 2 mm.
Anode capacitor of variable capacitance C18 - from UHF-66 (one section is used), the gap between the plates is 2.5-2.7 mm, the capacitance is 15-100 pF. The left (according to the diagram) terminal of the capacitor is connected to the 1-2nd turn of the coil l 2.
Antenna variable capacitor C7 - 2-3 sections, from old radios, the gap between the plates is 0.3-0.4 mm, capacity - 30-1200 pF.
Relay K1 - REN-33, K2 - REN-34; KZ-K5 - imported, small-sized (15x15x20 mm, in plastic cases) for an operating voltage of 12 V, switching current - 6-8 A for a voltage of 125-220 V; Kb-K13 - RES-10. Relay for connecting additional capacitors to the anode capacitor 220 pF (1.8 MHz) and 150 pF (3.5 MHz) - TORN type.
Halogen lamp vl 3 - 150 W / 220 V. Transistor vt 1 - KT835 (KT837), vt 2 - vt 4 - KT829A. Chip da 1 - KR142EN9I (78l 24).
The power amplifier is made in a computer case (preferably an old one, from the 80s, made of thick steel). Overall dimensions - 175 mm (width), 325 mm (height) and 400 mm (depth). Vertical partition and horizontal shelves: - steel, 1.5-2 mm thick. In the middle (along the center line) in the P-circuit compartment and under the GK71 panel there is a copper strip 10-12 mm wide and 0.2-0.3 mm thick, which is connected to the “Housing” terminal on the rear panel.
The surge protector is made on a separate board installed near the VA-47 machine and the “Network” connector. Between the power transformer and the vertical partition, a board of high-voltage rectifiers, stabilizers and automation is installed vertically, which is attached to the bottom of the case on an aluminum corner, which also serves as a radiator for the stabilizer da 1, vt 1 and vt 2.
On the inside of the front panel there are fixed: a voltage indication board for the control and screen grids, a high voltage and a halogen lamp, and its glow should be visible through the hole (a 03 mm red filter is installed) located near the “Anode” toggle switch.
In order to increase reliability, the outer board of the range switch, which switches the coil taps, is additionally insulated from the fastening screws with fluoroplastic bushings.
On the measuring device, directly on its terminals, a board is attached to the unit for measuring the output RF voltage.
First, without applying voltage from the step-up winding to the high-voltage rectifier, check the presence of filament voltage, relay power (+24 V), GK71 lamp locking (-60-70 V) and screen grid power (+1-55 V); fan operating modes(rx - 7-8 V, TX - 10-12 V), as well as the operation of the switching unit"rx/tx".
Next, connect the high-voltage winding to the rectifier. At idle, the constant anode voltage should be 2.8-3 kV. Adjusting the resistor resistance r14 establish clear operation of relay K4 at a mains voltage of 200 V.
Then adjust the resistor resistance r 1 8 in TX mode set the quiescent current of the GK71 lamp within 50-60 mA.
The RF tuning of the amplifier begins with the “cathode” circuit. In transmission mode from the transceiver (with the antenna tuner turned off), a signal with a power of 5-10 W is supplied and the SWR is adjusted to a minimum, focusing on the readings of the SWR meter of the transceiver. In the 28 MHz range, the “cathode” circuit is adjusted by adjusting the capacitance of capacitor C22. Then, by adjusting the capacitances of capacitors C13-C16 and selecting the capacitance of capacitors C11 and C12, this circuit is tuned to the lower frequency ranges of 7-24 MHz.
Setting up the output P-circuit also begins with the 28 MHz range. To do this, taking precautions, move or move apart the turns of the coil l 4, and also adjust the capacitances of capacitors C7 and C18. After tuning, applying the full input power of 60-80 W to the amplifier input, the “cathode” and then the P-circuit are again adjusted. The maximum anode current can reach 0.45-0.5 A.
It should be noted that without changing the circuit, two GK71 lamps can be installed in the amplifier, correspondingly increasing the power of the Tr1 transformer and the dimensions of the device itself.
Section: [High Frequency Power Amplifiers]
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Once upon a time we lived, we didn’t grieve
Two nesting dolls, two lamps,
Not just any bugs, but geeks,
Seventy-one, cuties.
(S.S. Gribovsky)
This is how they would have lived if they hadn’t fallen into my hands. Moreover, a diagram taken as a basis caught my eye:
This determined their future fate. I decided to assemble this miracle device. I set myself the task of using available components whenever possible and thereby reducing the cost of the design. Basically, I did everything according to the author’s description, but refused to use expensive B1B vacuum contactors, using a biscuit switch converted according to Benzar to switch the taps of the P-circuit coils, and used a variometer coil from RSB-5 bl.3 as L8. The anode choke is designed and made according to RV4LK, the cathode choke is wound on a core from a fuel assembly with a permeability of 3000 nn. To connect additional capacity to the hot end on the 160m range, a firecracker relay from RSB-5 is used. Power transformer from the IKV-4 medical equipment (too weak in terms of power). The output relay TKE56POD is mounted on foam to reduce the audibility of operation clicks. The power supply (assembled in a case from a minitower computer) and the amplifier itself are made in different cases, based on the location conditions in the shack. KPI adjustment knobs for 10 and 8 mm are made from the lids of jars of cosmetics. To model the arrangement of elements in a body with given dimensions, I used the AUTOCAD program. The result of creativity is in the photo below.
Amplifier (535x320x185mm):
Power supply (175x400x335mm):
73 and success in your creativity!
RA2FN, Sergey.
Work on mistakes:
Six months later, the P-circuit switch, made according to Benzar, burned out. Instead, I installed a modified ceramic switch from RSB-5 (I used a movable group of contacts from two identical switches). It turned out to be a good 6-position contactor with self-cleaning contacts. 3 years - normal flight.
Also, we had to abandon the use of the TKE relay in the bypass circuit. It is bulky and very noisy, and the response time is too long for the QSK mode. I installed a reed contact with a homemade winding for the output switching. The result is a reed relay (works in tandem with RES-48 at the input). Works quickly, quietly, reliably. For three years there were no failures.
In the power supply, I replaced the previously used (and lost in the anode circuit) KD202R diodes with imported 10A7 ones. Good, powerful diodes. It is possible, and even better, to use 10A10.
19.11.2014RA2FN, Sergey.
Discuss on the forum
An excellent grounded grid amplifier for everyday use.
The input signal goes to the coaxial jack XW1 ("Input"). In reception mode and when the amplifier is turned off, this signal, through relay contacts K 1.1 and K6.1, is supplied to the output jack XW2 (“Output”), connected to the radio station antenna. To switch to the transmission mode, a control signal with level 0 is supplied to the XS1 socket (or, which is the same, the left - according to the diagram - terminal of the K8 relay winding is connected to the common wire). As a result, relays K1 and KB are activated, and the amplified signal through one of the P-circuits introduced into the path by the range switch SA1 (sections SA1.1 and SA1.2) enters the cathode circuit of the lamp VL1, connected according to a circuit with grounded grids. When switched on in this way, the GK-71 lamp turns into an ideal triode with a right-hand characteristic - current flows through it only when the voltage on the grids is positive (relative to the cathode). Its input impedance at the first harmonic of the signal in this case is close to 400 Ohms. To reduce the input resistance of the amplifier to 50 Ohms (it is at this load resistance that the “branded” transceiver delivers maximum power), P-circuits with a transformation ratio (increase) of the input voltage by a factor of two are used at the input.
The filament-cathode of the lamp is fed through a dual inductor E10E11, and the voltage supplied to them is approximately 12 V, which provides the quiescent current required for linear operation of the amplifier while maintaining a long lamp life.
The anode circuit of the lamp includes a conventional P-circuit C19L10-L12C20, the coil sections of which are switched by powerful high-frequency contactors K2-K5, controlled in turn by section SA1.3 of the range switch. Resistor R1, shunted by coil L9 with a small inductance, prevents self-excitation of the amplifier at VHF frequencies (and this possibility exists despite the mythical “low frequency” of the GK-71).
At the output of the P-circuit, an indicator of the output signal level is connected through a voltage divider R2R3 (elements VD1, C21, R4, C22, PA1). The required sensitivity of the indicator is set depending on the actual input impedance of the antenna by selecting resistor R4.
The operation of the amplifier is controlled by a signal from the transceiver through switch SA2. In its "Off" positions and "H" (heat) the amplifier does not work. In the "On" position the control signal turns on relay K8. The winding of this low-power relay is powered by a voltage of 12 V, which makes it possible for the amplifier to work with any “branded” transceiver (some of them have a very “weak” control circuit for an external power amplifier).
The amplifier's power supply consists of three unified small-sized transformers (T1-TZ) and two rectifiers. One of them (VD1) powers the relay windings and contactors, the other (VD2-VD5) powers the anode circuit of the lamp. Since anode transformers with a total voltage of the secondary windings of about 1750 V are not produced, the secondary windings of two transformers (T2 and T3) had to be connected in series. The incandescent circuit of the VL1 lamp is powered by the secondary windings of transformer T 1 connected in series. An axial fan electric motor M 1 with a rated voltage of 220 V is connected to part of its primary winding. It is only necessary for the amplifier version described below in a small-sized housing.
Details and design. The amplifier's power supply uses transformers TPP285 127/220-50 (Tl), TA285 127/220-50 (T2) and TA238/127-50 (TZ). The operating voltage of all relays (except for K8) and contactors is 24 V (relay K8 is 12 V with a winding resistance of at least 500 Ohms). The contacts of high-frequency relays K1 and Kb must be designed for switching power of 100 and 500 W, respectively, and they (the contacts) must operate normally in receive mode, i.e., at a voltage of the order of fractions of a microvolt. The contacts of contactors K2-K5 must be designed for a current of up to 10 A at a voltage of up to 3000 V, and the contactor K7 - for the same current at a voltage of 220 V. The switched current and voltage of relay K8 are 1 A and 24 V, respectively.
When selecting variable capacitors C 19 and C20 for an amplifier, it should be borne in mind that the gap between the plates of the first of them must be at least 2 mm, and the second (if the antenna has an input impedance of 50...100 Ohms) - at least 0. 3 mm. If an antenna with a higher input impedance is used (for example, a “beam” or “American” type), the gap between the C20 plates must be at least 1 mm.
The coils of the input P-circuits L1-L7 are wound with PEV-2 1.0 wire on fluoroplastic frames with a diameter of 10 mm. The winding is continuous, turn to turn, but it should be possible to move them apart when setting up the amplifier. The number of turns of these coils is as follows: L1-L3 - 12 each, L4, L5, L6 and L7 - 14, 20, 25 and 40, respectively. Coil L9 contains four turns of the same wire, evenly distributed along the length of the body of the resistor R1 (MLT-2 ).
The L8 choke is wound on a fluoroplastic frame with a diameter of 21 mm. Its winding is made of PEV-2 0.35 wire and consists of five sections (the gaps between adjacent sections are 3 mm): the first (counting from the terminal connected to resistor R1) contains 24 turns, evenly distributed over a length of 15 mm, all the rest ( second third, etc.) are wound turn to turn and occupy a length of 10, 15, 20 and 30 mm, respectively.
The magnetic core of the dual inductor L10L11 is three ferrite (600NN) rings of standard size K32x20x5 folded together. After wrapping it with varnished fabric tape, seven turns of MLP wire with a cross section of 0.75 mm2 are wound on it, folded in half and twisted with a pitch of about 10 mm.
The L10 output P-circuit coil is wound on a ribbed ceramic frame with a diameter of 40 mm and contains 4.5 turns of silver-plated copper wire with a diameter of 3 mm, the winding length is 25 mm (the high quality factor of this coil ensures full output power when operating in the 10 m range). The L 11 coil is made on the same frame. Its winding consists of eight turns of silver-plated wire with a diameter of 2.5 mm (winding length - 40 mm), the tap is made from the third turn, counting from the terminal connected to L10.
The cylindrical frame of the L12 coil is made of fluoroplastic. Its diameter is 40 mm. The coil contains 25 turns of PEV-2 1.5 wire, wound turn to turn (the tap is from the 11th turn, counting from the terminal connected to L11).
A small-sized version of the amplifier is assembled in a housing with dimensions (width x height x depth) - 280x280x320 mm. At a height of 140 mm, it contains a chassis with a hole for a GK-71 lamp installed in the rear right corner. The upper compartment contains parts of the output P-circuit and the dial meter PA1. The lower compartment contains the parts of the power supply, the PA2 device for indicating the anode current, switches SA1, SA2 and parts of the input P-circuit. A fan is mounted on the back wall of the lower compartment. The air flow passes through the annular slot formed by the lamp body and the walls of the hole for it in the chassis, into the upper compartment with a lid having a grille above the lamp.
In the second version of the amplifier design, there is no fan, but the width of its housing is increased to 400 mm (with the same height and depth). All parts are installed on a chassis 60 mm high, only switches SA1, SA2 and parts of the input P-circuits are mounted under it. To cool the amplifier, there is a grilled hole in the bottom of the case, and the lid is raised above the top wall to a height of 20 mm.
Setting up the amplifier begins with checking the functionality of the power supply. By setting switch SA2 to position "H", measure the voltage at the output of rectifier VD1, at the lamp filament terminals, at the output of rectifier VD2-VD5. The latter at idle (no load) should be about 2300, and with a load current of 400 mA (maximum current through the GK-71 when the amplifier is operating) - 2000 V.
Next, turn on the amplifier (SA2 - in the “On” position) and measure the quiescent current of the lamp, which should be about 30 mA. Do not forget to connect an equivalent load to the amplifier output, for example, a 500 W incandescent lamp with a voltage of 220 or 127 V. Then connect the signal source to the amplifier input via an SWR meter. Its output power must be sufficient to operate the SWR meter (2...10 W). By changing the winding length of the coils of the input P-circuits, we achieve an SWR at the input in the middle of each range, close to 1. In the ranges of 10 and 12 m (in which, as can be seen from the diagram, one input circuit operates), the minimum SWR is achieved at a frequency of 26 MHz ( in this case, its value at the edges of the ranges will be no more than 1.5). Finally, connect the antenna with which the amplifier will work, and, by manipulating capacitors C 19, C20, achieve maximum readings of the PA1 output indicator in each range. To quickly switch from range to range during operation, it makes sense to compile a table of the corresponding positions of the rotors of these capacitors.
Operating ranges are 10, 12, 15, 17, 20, 30, 40 and 80 m, peak output power in the absence of noticeable distortion of the amplified signal is 500 W, input impedance is 50 Ohms.
The power amplifier (PA) is made on the “old” reliable GK71 lamp, with a graphite anode that does not require airflow. Schematic diagram shown in Fig. 1.
The scheme is classic with a common grid (OS). Anode voltage - 3 kV, screen grid voltage - +50 V, filament voltage - 22 V, in “Sleep mode” - 11 V. Quiescent current - 100 mA. Drive power Pvx - 50-80 W.
Power delivered to the equivalent load of 50 Ohms Pout = 500-700 W.
The features of this mind scheme are:
- introducing a protection circuit against overcurrent and short circuit (SC) and maintaining a “Sleep mode” in the PA;
- use of a cathode resonant circuit for better matching with imported transceivers;
- original P-circuit circuit, which allows you to obtain the same output power on all ranges.
Rice. 1. Schematic diagram of a power amplifier based on GK71 with a common grid.
The PA is powered from one powerful transformer made on a torus. A high anode voltage of 2.5-3.0 kV is obtained by doubling the voltage taken from the step-up winding of the transformer.
When the PA is turned on, the 220 V mains voltage, passing through the line filter Lf, C42, C43, the circuit breaker SA4, is supplied to the primary winding of the transformer through the halogen lamp HL1. This ensures “soft” switching and extends the service life of the VL1 GK71 lamp and other PA elements.
After charging the capacitors, part of the high voltage removed from the divider R13-R18 and the potentiometer R12 is supplied to the automation circuit made on the TZ transistor. If there is no short circuit in the UM circuit, the voltage is normal, then the TZ opens, the Kb relay is activated, closing the halogen lamp HL1 with its contacts K6.1.
A feature of this automation scheme is the “small hysteresis” of the activation/release of the KB. This provides reliable protection of the PA from overcurrent of the anode or short circuit in the secondary circuits, breakdown and short circuit in the transformer windings, during which the TZ is closed, the CB is de-energized and the network winding of the transformer is connected to the network through the HL1 lamp, protecting the failure of the PA elements.
In standby mode, the GK71 lamp is supplied with a partial filament voltage of 11V. This ensures low heating of the lamp, the PA as a whole and the “Sleep mode” of the PA. When switching to “TX”, a full filament voltage of 22 V is supplied to the GK71, and after 0.2-0.25 s the PA is ready to operate at full power, which is an undoubted advantage of direct-heated lamps GK71, GU13, GU81.
To fully harmonize the PA with imported transceivers, a “Cathode circuit” is used, tuned to resonance on each band by connecting capacitors to L1 using relays K9-K13 on the ranges 10-24 MHz.
Initially, circuit L1 is tuned to the 28 MHz range with capacitor C21. On the low frequency ranges of 3.5 and 7 MHz, for more complete matching (due to the narrow-bandwidth of the cathode circuit L1C), the signal is fed through the contacts of relay K7 to the cathode three-winding choke - Dr1. In this case, to eliminate the influence, L1 is short-circuited along the HF side with capacitor C14 through contacts K8.1.
The SWR at the PA input does not exceed 1.5 on all bands and matches well with any imported transceiver, even without a tuner.
The output P-circuit of the PA is switched by a 3-board switch SA1. SA1.3 - switches the coil taps and connects an additional capacitor C23 to KPI C22 for communication with the antenna on the 3.5 MHz range.
Switch SA1.2 short-circuits the 3.5 MHz coil. Switch SA1.1 switches range relays. If the 1.8 MHz range is planned, then you need to add another relay and use the 9th position on switch SA1.
In the 28 MHz range, coil L4 operates, which is located directly in the GK71 anode circuit. This made it possible to obtain the same Pout at 28 MHz as on the low frequency ranges. Dr3 is necessary to protect the output circuits of the PA.
“RX/TX” control is carried out by a circuit on transistor VT1, which is powered by a voltage of +24 V. When the RX/TX input of connector XS1, pin 3, is closed to the housing (current 3-5 mA), the circuit on transistor T1 opens, the short-circuit relay is activated and through contacts K3.1, +24 V voltage is supplied to relays K1 and K2. Relay K4 is activated, supplying full filament voltage to GK71 through contacts K4.1.
If switch SA3 “Filament” is turned on, full filament voltage is constantly supplied to lamp VL1. This may be necessary when working in TESTax. After charging capacitor C3 (after 0.15-0.2 s), relay K5 will operate, which provides:
- correct operation of the mind;
- no burning of relay contacts K1, K2.
Relay K5 with contacts K5.1 closes the control grid circuit of the VL1 lamp to the housing, opening it. To implement the “Bypass” mode, switch SA2 breaks the +24 V power supply circuit of the circuit at?T1 of the “RX/TX” switching. Transistor T2 contains an adjustable voltage stabilizer for the screen grid of the VL1 lamp.
Potentiometer R4 sets the quiescent current VL1 in the range of 100-120 mA. The DA1 chip contains a +24 V voltage stabilizer to power the relay and automation circuit. During overloads and short circuits at +24 V, DA1 is automatically turned off, which also increases the reliability of the PA as a whole.
Power amplifier design
The mind is made in a housing system unit computer, preferably an old one from the 80s - it is made of thicker steel. Dimensions 175x325x400 mm. The vertical partition and horizontal shelves are made of steel with a thickness of 1.5-2 mm.
When the PA is operating intensively, it is advisable to use a fan operating at a reduced supply voltage to reduce noise.
Parts and possible replacements
Transformer T1 is made on iron from LATR-8 10 A. The network winding is wound with 1.5 mm PEL wire. Step-up winding PEL 0.65-0.7 mm, voltage 1.1-1.2 kV. The filament winding is PEL 1.5 mm 11+11 V, the remaining windings are PEL 0.5-0.65 mm for voltages 22 V and 50 V.
SA4 circuit breaker type VA-47 for 10 A. The cathode choke Dr1 is wound on a ferrite ring K45x27x15 mm 2000NN in two wires 1.2-1.5 mm and contains 12 turns. The communication coil has 7 turns of MGTF0.2 mm wire, evenly distributed between the turns of the main winding.
Coil L1 of the cathode circuit is made of a copper tube with a diameter of 5-6 mm. Inside of which there is a wire in heat-resistant insulation MGTF, BPVL with a cross-section of at least 1 mm2. The outer diameter of the coil is 27-30 mm, the gap between the turns is 0.2-0.3 mm and contains 8 turns, the outlet is from the middle.
The L2 coil of the 3.5-7 MHz range is made on a frame with a diameter of 40-45 mm and contains 15+12 turns of 1.5-2.0 mm wire. The first 15 turns for the 3.5 MHz range are wound turn to turn, and the remaining 12 turns are wound with a pitch of 2.5 mm.
The L3 coil of the 10-21 MHz range is made of a copper tube with a diameter of 5-6 mm and contains 15-17 turns, an outer diameter of 50-55 mm.
The L4 coil of the 28 MHz range is made of copper wire with a diameter of 2.0-2.5 mm and contains 5-6 turns, the outer diameter of the coil is 25 mm.
The anode choke Dr2 is wound on a fluoroplastic frame with a diameter of 18-20 mm, a length of 180 mm, with PELSHO wire 0.35 mm, turn to turn in sections 41+34+32+29+27+20+17+11 turns and the last 10 turns in discharge in 2 mm increments.
Dr3 - universal winding with PELSHO wire 0.2-0.3 mm, 2-4 sections of 80-100 turns.
The Lf surge protector is wound on a K45x27x15 mm 2000NN ring in two wires with a diameter of 1 mm, with good insulation of the MGTF type, turn to turn until filled.
Anode KPE S24 from UHF-66. One section, gap 2.5-2.7 mm 15-100 pF, connected to the 2nd turn of coil L3. Capacitor C23 - connection with the antenna KPE 2-3 sections from old radios with a gap of 0.3-0.4 mm, 30-1200 pF.
Relay K1 - REN-33, K2 - REN-34. Relay KZ-K6 - small-sized imported in plastic cases 15x15x20 mm, switching current 6-8 A, switching voltage 127-220 V. Relay KZ and Kb for an operating voltage of 24 V, and relays K4 and K5 for an operating voltage of 12 V. Relay K7 -K13 - RES-10 low-power silicon diodes are connected in parallel to the relay windings. The diodes are not shown in the diagram.
Transistors VT1 - KT835, KT837. VT2, VT3 - KT829A. DA1 - KR142EN-9 (B, D) or MS7824.
Each time the “TX” mode is turned on, the voltage from the collector of transistor VT1 through resistor R3 opens transistor VT8 and discharges capacitor C6. But if it manages to fully charge, the composite transistor VT10VT11 opens and closes the base circuit of the transistor VT4 to a common wire. The transistor closes, relay K3 is de-energized and the glow of the GK-71 lamps is turned off. The fans are also turned off, and the network windings of transformers T1, T2 are reconnected through lamp EL1, and the HL4 “Sleep” indicator LED lights up.
In this mode, the PA consumes no more than 50 W of power and can remain in constant readiness for use for as long as desired. It is enough to press the pedal, and after 1 second it is ready for active work at full power!
The power supply for all relays and automation components is provided by a doubler rectifier using diodes VD11, VD12 and capacitors C23, C24.
Switch SA3 selects the filament voltage of lamps VL1, VL2 22 V or 17 V, and switch SA2 constantly supplies the full filament voltage, which is sometimes necessary when working in contests.
The unit on transistor VT3 serves to protect against breakdown and burning of the rotor/stator plates of capacitor C1 (for example, in the event of a break in the antenna). If an RF voltage of more than 300 V appears on the capacitor, it will go through a divider on resistors R46, R47 and diode VD27 to the base of transistor VT3, which will open, shunting the base of transistor VT4, and the amplifier will switch to “Sleep” mode. The protection threshold is regulated by trimming resistor R48.
The amplifier is assembled in a vertical housing with dimensions 240xx420x420 mm (Fig. 2). Its frame is welded from steel angle 15x15 mm, which gives the case the necessary strength. The internal volume of the frame is divided in half by a vertical partition, which, in turn, is divided at a height of 220 mm from the bottom by a horizontal subchassis. All components and parts of the amplifier are located in the resulting four compartments (Fig. 3). This arrangement provides convenient access to installation and good cooling of the elements.
Rice. 2. Amplifier assembly
Rice. 3. Units and parts of the amplifier
On the front panel of the amplifier there are controls, indications and controls. The axes of the trimming resistors are located “under the slot” below the level of the “PWR”, “QRP”, “TUNE” toggle switches. On the rear panel there are RF connectors XW1, XW2, a ground terminal, connector X1 "PTT", fans.
All RF connectors, ground terminal, blocking capacitors and KPE C1, C31 are connected to each other by a 15x0.5 mm copper strip running along the center line between the front and rear panels.
Coil L1 is wound with a copper tube with a diameter of 5 mm on a mandrel with a diameter of 50 mm. The number of turns is 10, the winding pitch is 8...12 mm. Its inductance is 2.8 μH. The coil taps are made from the 3rd, 4th, 6th and 8th turns, counting from the terminal connected to the capacitor C30. Coil L2 is wound with PEV-2 1.5 wire on a ceramic frame with a diameter of 50 mm. Number of turns - 27, inductance - 24 µH. The taps are made from the 3rd, 8th, 15th turns, counting from the terminal connected to the L1 coil.
Coil L3 - four sections of 80 turns each, wound "Universal" with PELSHO 0.2 wire on a ceramic frame with a diameter of 8 mm. The distance between sections is 2.5 mm. Inductance - 250...350 µH.
Low-pass filter coils L4, L5 are wound with PEV-2 0.7 wire on a mandrel with a diameter of 8 mm. Number of turns - 10, inductance - 1.1 µH.
The anode choke L10 is similar in design to the choke from Um "Ameritron". It is wound with PETV-2 0.38 wire on a ceramic frame with a diameter of 24 mm and a length of 180 mm. Winding - turn to turn, sectional - 82+55+42 turns. The distance between sections is 20 mm. After winding, the sections are impregnated with insulating varnish or BF-2 glue.
Line filter coils L11, L12 are wound halfway from the magnetic core of the TVS-110 transformer. Winding - bifilar with MGTF1.0 wire until filled.
The anode transformer T1 is made on a toroidal magnetic core from LatR-1M/9 A (overall power - 2 kW). Network winding I contains 240 turns of PETV-2 1.4 wire. The no-load current should not exceed 0.3 A. High-voltage winding II (1100 V) - 1250 turns with PETV-2 0.67 wire. Winding III of the screen grid power supply (270 V) - 580 turns with PEV-2 0.45 wire.
The power of transformer T2 must be at least 200 W. The voltage of winding II is 100 V, winding is with a wire with a diameter of 0.2...0.3 mm, the voltage of winding III is 21 V, the wire is with a diameter of 0.7 mm. Winding IV (power supply for incandescent lamps) - 22 V (taps from 17 V and 10 V), wire - 1.5 mm in diameter.
Transformer T3 is made on a toroidal magnetic core OL 70x40x20 mm (from an industrial current transformer). Its primary winding contains three turns of PEV-2 1.4 wire, distributed evenly around the perimeter. The secondary winding is 75+25+25+25+25+25 turns with PEV-2 0.45 wire.
The T4 HF transformer is made on a ring magnetic core of standard size K20x10x5 mm from ferrite grade 200-400NN. Winding II contains 20 turns of PETV-2 0.38 wire. Winding I is a wire passed through the hole in the magnetic circuit and connecting connector XW2 to the switching contact of relay K2.1.
The T5 transformer is wound with PEV-2 0.7 wire on a ring magnetic wire of standard size K30x20x6 mm made of VC20 grade ferrite. Winding - in three twisted wires with a pitch of two twists per centimeter. Number of turns - 10.
Due to the large scatter in the parameters of domestic ferrites, the number of turns and twist pitch are selected during setup.
All relays in the amplifier are for a rated voltage of 24 V. Relays K1, K3 - REN33, K2 - REN34. Circuit breaker SF1 - BA47-29. Fan M1 - dimensions 120x120x32 mm, rated voltage 48 V (current consumption - 0.25 A), for example, D1238E48V or EFB1248HF. Fan M2 - for a voltage of 12 V (at a current of 0.15 A) with dimensions of 80x80x20 mm from a computer power supply. Measuring instruments RA1, RA2 - M42300 with a full deflection current of the arrow of 1 mA and 1 A, respectively.
Capacitor C1 is a two- or three-section CPE from a broadcast receiver (the gap between the rotor and stator plates is at least 0.3 mm). All sections of the capacitor are connected in parallel. Anode KPE S31 - from the UHF-66 physiotherapeutic device (one section was used), the gap between the introduced rotor and stator plates is at least 0.8 mm. Capacitors C15-C17, C29, C30 - KVI-3 and K15 series. Blocking capacitors - KSO or K31-11. Trimmer capacitors C12 and C13 - KPK-MP. All oxide capacitors are imported.
High-voltage rectifier capacitors C25 and C26 - K75-40b 100μFx2kV. They can be replaced by ten oxide capacitors with a capacity of 470-680 μF for a rated voltage of 400-450 V, connected in series. To equalize the voltage, each capacitor should be bypassed with an MLT-2 220 kOhm resistor.
Switch SA1 is used from the R-130 radio station, which has undergone modernization: a common silver-plated current collection contact has been introduced, after which the switch can withstand a power of 2...2.5 kW, a fixation has been made for ten positions, and the common moving contacts are 2nd and 3rd The biscuits are connected axially to the switch body, which made it possible to switch additional capacitors on the 1.8, 3.5 and 7 MHz ranges.
Most of the resistors in the amplifier are MLT or CF-2 W. Resistor R44 is non-induction TVO-10. All trimming resistors are SPO-0.5, SP4-1A. Thermistor RK1 - MMT-4.
Halogen lamp EL1 - 250-500 W/220 V, diameter 8 mm and length 78...115 mm. The lamp is installed in a standard ceramic holder on the back of the amplifier's front panel. To make its glow visible, a hole with a diameter of 3 mm was drilled in the panel.
Indicators HL1-HL3 - imported neon N-814 for 220 V, red, green and blue. LED HL4 - imported, blue light.
Transistors VT1, VT4, VT5 are installed on heat sinks with an area of 25 cm 2.
Most of the amplifier parts are mounted on printed circuit boards. The power meter board is fixed to the contact pins of connector XW2, and the axis of the trimming resistor R49 (calibration of PA1 readings) is located on the rear panel “under a slot” next to the connector.
The initial setup of the amplifier is carried out without connecting the anode transformer T1 to the network and disconnecting its winding II from the rectifier, as well as disconnecting winding II of the transformer T2 from the rectifier. First, they check the presence of source voltages +48 V/+24 V and the incandescence of GK-71 lamps, then they check and adjust the operation of the automation units and select the optimal operating modes for the fans. By heating the thermistor RK1 to a temperature of 100 o C, the trimming resistor R13 sets the threshold for a sharp increase in the fan speed. The maximum fan speed is set with trimming resistor R19, the minimum - R17. The resistance of resistor R51 is chosen such that the voltage on fan M2 does not exceed + 13 V in “TX” mode. To check the operation of the automatic protection, a voltage of +24 V is applied to the base of the transistor VT4 through a 22 kOhm resistor (without turning off the other circuits) and the threshold for clear operation (switching off) of relay K3 is set using trimming resistor R28.
GK-71 lamps, especially those that have been left unused for a long time, should be subjected to “training” by keeping them under incandescent voltage for 12...20 hours, after which the emission of the lamps, as a rule, is restored.
Next, connect winding II of transformer T2 to the rectifier and check the operation of the voltage stabilizer of the first grid. The bias voltage must be regulated by trimming resistor R22 within the range of -90...-130 V at a current of 8...10 mA, which is measured at the contacts of relay K1.2. Then transformer T1 is connected to the network and the voltage on the screen grids of the lamps is measured, which should be +650...+700 V. If necessary, the taps of winding II of transformer T3 are phased and selected according to the best voltage stabilization of the second grid.
And last but not least, FOLLOWING PRECAUTIONS, check the high voltage rectifier. First, a voltage of 270 V is applied to it from winding III and the voltage distribution across the capacitors is measured. Only after this is the full voltage supplied from the high-voltage winding I of transformer T1. The voltage at the rectifier output should be 3100...3300 V without load, and under a load of 0.6 A - 2900...3000 V.
If all voltages are normal, the amplifier is switched to the “TX” mode and the quiescent current of the lamps is set within 140...150 mA.
It is extremely important to check the amplifier for the absence of self-excitation in the “Setup” and “Operation” modes, as evidenced by sharp jumps in the quiescent current and the operation of automatic protection in all ranges and at different positions of the rotors of capacitors C1, C31. As an indicator of self-excitation, it is convenient to use a neon lamp MH-3, mounted on an insulated stick, bringing it to the VKS elements. Only after eliminating self-excitation, if any, can you proceed to further adjustment of the mind.
The input circuits and low-pass filters are adjusted by selecting the number of turns of transformer T5 and adjusting capacitors C12, C13, achieving uniform swing of the lamps on all ranges (especially on the 28 MHz range) with a signal power from the transceiver of 15...20 W.
By connecting the equivalent of a load of 50 (75) Ohms with a power of 1...2 kW to the output of the amplifier, and a protective ground to the housing, a signal with a power of 5...10 W from the transceiver is supplied to the input of the amplifier. The P-circuit is configured in the HF bands by selecting the taps of the L1 coil, one by one, starting from the 28 MHz range. The capacitance of capacitor C31 should be
to be close to the minimum. On the 14 MHz band, the entire coil winding is used. Then, by selecting the taps of the coil L2 and capacitors C15-C17, the P-circuit is tuned in the low frequency ranges.
The output power meter can be adjusted without connecting the amplifier to the network. It is enough to apply a 100 W signal from the transceiver to the PA input and connect the equivalent of 50 Ohms instead of the antenna.
Having completed the preliminary setup, a signal with a power of 20...30 W is supplied to the PA input and the VKS is adjusted again. With an output power of 1 kW, the anode current can reach 550...600 mA.
Publication date: 03.07.2018
Readers' opinions
- Vladimir / 07/10/2019 - 08:33
my email [email protected] - Vladimir / 07/10/2019 - 08:30
Is it possible to write off about repeating the mind on 2 GK71
