Encyclopedia of radio electronics and electrical engineering / radio reception

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Recently, there has been a great interest in antique and retro radio equipment. The items of the collections are both copies of retro radio equipment of the 40-60s, and real antique devices of the 10-30s of the last century. In addition to collecting original items, there is a growing interest in collecting and making so-called replicas. This is a very interesting direction of amateur radio creativity, but first let's explain the meaning of this term.

There are three concepts: original, copy and replica of an antique item. The term "original" needs no description. A copy is a modern repetition of an antique product, down to the smallest details, materials used, design solutions, etc. A replica is a modern product made in the style of products of those years and, if possible, with approximate design solutions. Accordingly, the closer the replica is to the original products in terms of style and detail, the more valuable it is.

Now there are many so-called radio souvenirs on sale, mostly made in China, decorated in the form of retro and even antique radio equipment. Unfortunately, upon closer examination, it is clear that its value is low. Plastic handles, painted plastic, body material - MDF pasted over with a film. All this speaks of a very low-grade product. As for their "stuffing", it, as a rule, is a printed circuit board with modern integral elements. The internal installation of such products in terms of quality also leaves much to be desired. The only "advantage" of these products is their low price. Therefore, they may be of interest only to those who, without going into technical subtleties or simply not understanding them, want to have an inexpensive "cool thing" on their desk in their office.

As an alternative, I want to present a receiver design that fully meets the requirements of an interesting and high-quality replica. This is a super-regenerative tube VHF FM receiver (Fig. 1), operating in the frequency range of 87...108 MHz. It is assembled on radio tubes of the octal series, since it is not possible to use lamps with a pin base, older and suitable in style, in this design due to the high operating frequency of the receiver.

Rice. 1. Super regenerative tube VHF FM receiver

Bronze terminals, control knobs and brass nameplates are an exact copy of those used in products of the 20s of the last century. Some elements of fittings and design are original. All radio tubes of the receiver are open, except for the screens. All inscriptions are made in German. The body of the receiver is made of solid beech. Installation, with the exception of some high-frequency nodes, is also made in a style as close as possible to the original of those years.

The front panel of the receiver has a power switch (ein / aus), a frequency setting knob (Freq. Einst.), a frequency scale with an arrow tuning indicator. The volume control (Lautst.) - on the right and the sensitivity control (Empf.) - on the left are displayed on the top panel. Also on the top panel there is a pointer voltmeter, the backlight of the scale of which is an indication of the power on of the receiver. On the left side of the case there are terminals for connecting the antenna (Antenne), and on the right side there are terminals for connecting an external classical or horn loudspeaker (Lautsprecher).

I want to note right away that the further description of the receiver device, despite the presence of drawings of all the details, is for informational purposes, since the repetition of such a design is available to experienced radio amateurs, and also implies the presence of certain wood and metalworking equipment. In addition, not all elements are standard and purchased. As a result, some installation dimensions may differ from those shown in the drawings, as they depend on the elements that will be available. For those who want to repeat this one-to-one receiver and who need more detailed information about the design of certain parts, assembly and installation, drawings are offered, as well as the opportunity to ask a question directly to the author.

The receiver circuit is shown in fig. 2. Antenna input is designed to connect a balanced VHF antenna drop cable. The output is designed to connect a loudspeaker with a resistance of 4-8 ohms. The receiver is assembled according to the 1-V-2 scheme and contains a UHF on the VL1 pentode, a superregenerative detector and a preliminary UHF on a VL3 double triode, a terminal UHF on the VL6 pentode and a power supply on a T1 transformer with a rectifier on the VL2 kenotron. The receiver is powered by 230 V.

Rice. 2. Receiver circuit (click to enlarge)

UHF is a range amplifier with a diversity tuning of the circuits. Its tasks are to amplify the high-frequency oscillations coming from the antenna, and to prevent the penetration into it and radiation into the air of its own high-frequency oscillations of the super-regenerative detector. UHF is assembled on a high-frequency pentode 6AC7 (analogue - 6Zh4). The connection of the antenna with the input circuit L2C1 is carried out using the coupling coil L1. The input impedance of the cascade is 300 ohms. The input circuit in the grid circuit of the VL1 lamp is tuned to a frequency of 90 MHz. The setting is carried out by selecting the capacitor C1. The L3C4 circuit in the anode circuit of the VL1 lamp is tuned to a frequency of 105 MHz. The setting is carried out by selecting the capacitor C4. With this configuration of the circuits, the maximum UHF gain is about 15 dB, and the frequency response unevenness in the frequency range of 87 ... 108 MHz is about 6 dB. Communication with the subsequent cascade (superregenerative detector) is carried out using the L4 coupling coil. Using a variable resistor R3, you can change the voltage on the screen grid of the VL1 lamp from 150 to 20 V and thereby change the UHF transmission coefficient from 15 to -20 dB. Resistor R1 serves to automatically generate a bias voltage (2 V). Capacitor C2 shunting resistor R1 eliminates AC feedback. Capacitors C3, C5 and C6 - blocking. The voltages at the terminals of the VL1 lamp are indicated for the upper position of the resistor R3 engine according to the diagram.

Super Regenerative Detector assembled on the left half of the double triode VL3 6SN7 (analogue - 6H8C). The super-regenerator circuit is formed by an inductor L7 and capacitors C10 and C11. The variable capacitor C10 serves to tune the circuit in the range of 87 ... 108 MHz, and the capacitor C11 - to "lay" the boundaries of this range. In the grid circuit of the triode of the superregenerative detector, the so-called "gridlick" is included, formed by the capacitor C12 and the resistor R6. With a selection of capacitor C12, a damping frequency of about 40 kHz is set. The connection of the super-regenerator circuit with UHF is carried out using the L5 coupling coil. The supply voltage of the anode circuit of the super-regenerator is supplied to the output of the loop coil L7. Inductor L8 - superregenerator load at high frequency, inductor L6 - at low frequency. Resistor R7 together with capacitors C7 and C13 form a filter in the power circuit, capacitors C8, C14, C15 are blocking. The AF signal through the capacitor C17 and the low-pass filter R11C20 with a cutoff frequency of 10 kHz is fed to the input of the preliminary ultrasonic frequency converter.

Preliminary ultrasound assembled on the right (according to the scheme) half of the triode VL3. The cathode circuit includes a resistor R9 for automatically generating a bias voltage (2,2 V) on the grid and a choke L10, which reduces the gain at frequencies above 10 kHz and serves to prevent the penetration of superregenerator quenching pulses into the final ultrasonic frequency converter. From the anode of the right triode VL3, through the coupling capacitor C16, the AF signal is fed to the variable resistor R13, which acts as a volume control.

Terminal UZCH assembled on a powerful pentode VL6 6F6G (analog - 6F6S). The low-frequency signal to the grid of this lamp comes from a variable resistor R13. Resistor R6 is included in the cathode circuit VL15, which serves to automatically generate a bias voltage of 17 V. To eliminate negative feedback on alternating current, resistor R15 is shunted by capacitor C21. To match the low-resistance dynamic head, an output transformer T6 with a voltage transformation ratio of 2:36 is installed in the anode circuit of the VL1 lamp. When connecting a dynamic head with a resistance of 4 ohms, the equivalent load resistance of the VL6 pentode is about 5 kOhm. The anode winding of the output transformer is shunted with capacitor C22, which serves to equalize the load resistance of the VL6 lamp, which increases at high frequencies due to the parasitic leakage inductance of the output transformer.

Power supply unit provides power to all components of the receiver: 6,3 V alternating voltage - to power the incandescent lamps, 250 V direct unstabilized voltage - to power the anode circuits of the UHF and the final ultrasonic frequency converter. The rectifier is assembled according to a full-wave circuit on a VL2 5V4G kenotron (analog - 5Ts4S). The rectified voltage ripple is smoothed out by the C9L9C18 filter. The supply voltage of the super-regenerator and the preliminary ultrasonic frequency converter is stabilized by a parametric stabilizer on the resistor R14 and gas-discharge zener diodes VL4 and VL5 VR105 (analogue - SG-3S). The R12C19 RC filter additionally suppresses voltage ripple and zener diode noise.

Construction and installation. UHF elements are mounted on the main chassis of the receiver around the lamp panel. To prevent self-excitation of the cascade, the grid and anode circuits are separated by a brass screen. Communication coils and loop coils are frameless and mounted on textolite mounting racks (Fig. 3 and Fig. 4). Coils L1 and L4 are wound with silver-plated wire with a diameter of 2 mm on a mandrel with a diameter of 12 mm with a pitch of 3 mm.

Rice. 3. Communication coils and contour coils are frameless, mounted on textolite mounting racks

Rice. 4. Communication coils and contour coils frameless, mounted on textolite mounting racks

L1 has 6 turns with a tap in the middle and L4 has 3 turns. Loop coils L2 (6 turns) and L3 (7 turns) are wound with silver-plated wire with a diameter of 1,2 mm on a mandrel with a diameter of 5,5 mm, the winding pitch is 1,5 mm. Loop coils are located inside the coupling coils.

The screen grid voltage of the VL1 lamp is controlled by a pointer voltmeter located on the top panel of the receiver. The voltmeter is implemented on a milliammeter with a total deviation current of 2,5 mA and an additional resistor R5. Subminiature scale backlight lamps EL1 and EL2 (CMH6,3-20-2) are placed inside the milliammeter case.

Rice. Fig. 5. Elements of the super-regenerative detector and preliminary USCH, mounted in a separate shielded block

The elements of the super-regenerative detector and the preliminary UZCH are mounted in a separate shielded block (Fig. 5) using standard mounting racks (SM-10-3). The capacitor of variable capacity C10 (1KPVM-2) is fixed on the wall of the block with the help of glue and a textolite sleeve. Capacitors C7, C8, C14 and C15 are pass-through series KTP. A choke L7 is connected through capacitors C8 and C6. The supply voltage to the shielded unit is supplied through the capacitor C15, and the filament voltage is supplied through the capacitor C14. Oxide capacitor C19 - K50-7, inductor L8 - DPM2.4. The inductor L6 is self-made, it is wound in two sections on a Sh14x20 magnetic circuit and contains 2x8000 turns of PETV-2 0,06 wire. Since the choke is sensitive to electromagnetic interference (in particular, from the elements of the power supply), it is mounted on a steel plate above the UHF (Fig. 6) and closed with a steel screen. It is connected with shielded wires. The braid is connected to the body of the super-regenerator unit. For the manufacture of the L10 inductor, an armored magnetic core SB-12a with a permeability of 1000 was used, a winding was wound on its frame - 180 turns of PELSHO 0,06 wire. Coils L5 and L7 are wound with silver-plated wire with a diameter of 0,5 mm with a pitch of 1,5 mm, on a ribbed ceramic frame with a diameter of 10 mm, which is glued using a textolite sleeve into the hole in the lamp panel. The inductor L7 contains 6 turns with a tap from 3,5 turns, counting from the top according to the output circuit, the coupling coil L5 is 1 turns.

Rice. 6. Choke mounted on a steel plate above the UHF

The shielded unit is attached to the receiver's main chassis with a threaded flange. The connection of the capacitor C16 and the resistor R13 is made by a shielded wire with the shielding braid grounded near the resistor R13. The rotation of the rotor of the capacitor C10 is carried out using a textolite axis. To ensure the necessary strength and wear resistance of the splined connection of the axis and the C10 capacitor, a cut was made in the axis, into which a fiberglass plate was glued. One end of the plate is sharpened so that it fits snugly into the slot of the capacitor C10. The axle is fixed and pressed against the slot of the capacitor by means of a spring washer laid between the bracket sleeve and the driven pulley fixed on the axle (Fig. 7).

Rice. 7. Shielded block

The vernier is assembled on two brackets fixed on the front wall of the shielded block of the super-regenerator (Fig. 8). Brackets can either be made independently, according to the attached drawings, or you can use a standard aluminum profile with minor modifications. To transmit rotation, a nylon thread with a diameter of 1,5 mm was used. You can use a "harsh" shoe thread of the same diameter. One end of the thread is attached directly to one of the pins of the driven pulley, and the other - to the other pin through the tension spring. Three turns of thread are made in the groove of the leading axis of the vernier. The driven pulley is fixed on the axis so that in the middle position of the variable capacitor C10, the end hole for the thread is located diametrically opposite to the leading axis of the vernier. Both axles are equipped with extension nozzles, fixed to them with locking screws. On the nozzle of the leading axis there is a frequency adjustment knob, and on the nozzle of the slave - a pointer scale indicator.

Rice. 8. Vernier

Most of the elements of the final ultrasonic frequency converter are mounted on the terminals of the lamp panel and mounting racks. The output transformer T2 (TVZ-19) is installed on an additional chassis and is oriented at an angle of 90^о in relation to the magnetic circuit of the inductor L9 of the power supply. The connection of the control grid of the VL6 lamp with the engine of the resistor R13 is made with a shielded wire with grounding of the shielding braid near this resistor. Oxide capacitor C21 - K50-7.

The power supply (except elements L9, R12 and R14, which are mounted on an additional chassis) is mounted on the main chassis of the receiver. Choke L9 unified - D31-5-0,14, capacitor C9 - MBGO-2 with flanges for mounting, oxide capacitors C18, C19 - K50-7. For the manufacture of the T1 transformer with an overall power of 60 V-A, a Sh20x40 magnetic core was used. The transformer is supplied with metal stamped covers. On the top cover there is a panel of the VL2 kenotron together with a brass decorative nozzle (Fig. 9). A mounting block is installed on the bottom cover, where the necessary outputs of the transformer windings and the output of the cathode of the kenotron are brought out. The power transformer is attached to the main chassis with studs that tighten its magnetic circuit. The stud nuts are four threaded posts, on which the additional chassis is fixed (Fig. 10).

Rice. 9. Kenotron panel VL2 with brass decorative cap

Rice. 10. Additional chassis

The entire installation of the receiver (Fig. 11) is carried out with a single-core copper wire with a diameter of 1,5 mm, placed in a varnished cloth tube of various colors. Its ends are fixed with a nylon thread or pieces of a heat-shrinkable tube. The assembly wires assembled in bundles are interconnected with copper brackets.

Rice. 11. Mounted receiver

Before installation, the transformer T1 and capacitors C13, C18, C19 and C21 are painted from a spray gun with Hammerite hammer black paint. The power transformer is painted in a contracted state. When painting capacitors, it is necessary to protect the lower part of their metal case, which is adjacent to the chassis. To do this, before painting, the capacitors can, for example, be fixed on a thin sheet of plywood, cardboard or other suitable material. At the power transformer, before painting, it is necessary to remove the decorative brass nozzle and protect the kenotron panel from paint with masking tape.

Chassis The receiver is wooden and made of solid beech. The side walls are connected with a tenon joint with a pitch of 5 mm. An understatement was made in the front of the case to accommodate the front panel. Rectangular holes are made in the side and rear walls of the case. The outer edges of the holes are processed with an edge radius cutter. On the inner edges of the holes, there are understatements for fastening the panels. Panels with contact input and output terminals are fixed in the side openings of the case, and a decorative grille is in the back. The upper and lower parts of the body are also made of solid beech and finished with edge cutters. All wooden parts are stained with a mocha stain, primed and varnished with professional paints and varnishes (LKM) from Votteler with intermediate grinding and polishing according to the instructions attached to these paintwork materials.

The front panel is painted with "Hammerite black smooth" paint using a technology that gives a large, pronounced shagreen (large droplet spray onto a heated surface). The front panel is fixed on the receiver body with brass self-tapping screws of appropriate sizes with a semicircular head and a slot. Similar brass fasteners are available in some hardware stores. All nameplates are custom made and CNC laser engraved on 0,5mm thick brass plates. They are mounted on the front panel with M2 screws, and on a wooden panel - with brass self-tapping screws.

After assembling the receiver and checking the installation for possible errors, you can proceed with the adjustment. To do this, you will need a high-frequency oscilloscope with an upper cut-off frequency of at least 100 MHz, a capacitor capacitance meter (from 1 pF) and, ideally, a spectrum analyzer with a maximum frequency of at least 110 MHz and a swept frequency generator (SFS) output. If the spectrum analyzer has a GKCh output, it is possible to observe the frequency response of the objects under study. A similar instrument is, for example, the SK4-59 analyzer. If this is not available, an RF generator with the appropriate frequency range will be required.

A properly assembled receiver starts working immediately, but requires adjustment. First check the power supply. To do this, the VL1, VL3 and VL6 lamps are removed from the panels. Then a load resistor with a resistance of 18 kOhm and a power of at least 6,8 W is connected in parallel with the capacitor C10. After turning on the power supply and warming up the kenotron VL2, the gas-discharge zener diodes VL4 and VL5 should light up. Next, measure the voltage across the capacitor C18. With an unloaded filament winding, it should be slightly higher than indicated on the diagram - about 260 V. At the anode of the zener diode VL4, the voltage should be about 210 V. The alternating voltage of the filament of radio tubes VL1, VL3 and VL6 (in their absence) is about 7 V. If all of the above above the voltage value is normal, the test of the power supply can be considered complete.

Unsolder the load resistor and install the VL1, VL3 and VL6 lamps in their places. The sensitivity control slider (resistor R3 is set to the upper position according to the diagram, and the volume control (resistor R13) is set to the minimum volume position. A dynamic head with a resistance of 3 ... 4 ohms is connected to the output (terminals XT4, XT8). After turning on the receiver and warming up all radio tubes check the voltage at their electrodes in accordance with those indicated in the diagram.When the volume is increased by turning the resistor R13, the characteristic high-frequency noise of the super-regenerator should be heard in the loudspeaker.Touching the antenna terminals should be accompanied by an increase in noise, which indicates the correct operation of all stages of the receiver.

Adjustment begins with a super-regenerative detector. To do this, the screen is removed from the VL3 lamp and a communication coil is wound around its balloon - two turns of a thin insulated mounting wire. Then install the screen back, releasing the ends of the wire through the top hole of the screen and connecting the oscilloscope probe to them. With the correct operation of the superregenerator, characteristic flashes of high-frequency oscillations will be visible on the oscilloscope screen (Fig. 12). By selecting capacitor C12, it is necessary to achieve a flash repetition rate of about 40 kHz. When tuning the receiver over the entire range, the burst repetition rate should not change noticeably. Then the tuning range of the super-regenerator is checked, which determines the tuning range of the receiver, and if necessary, it is corrected. To do this, instead of an oscilloscope, a spectrum analyzer is connected to the ends of the coupling winding. A selection of capacitor C11 lays the boundaries of the range - 87 and 108 MHz. If they are very different from those indicated above, it is necessary to slightly change the inductance of the coil L7. At this point, the setting of the super-regenerator can be considered complete.

Rice. 12. Oscilloscope readings

After adjusting the super-regenerator, the coupling coil is removed from the VL3 lamp bulb and proceed to the establishment of UHF. To do this, it is necessary to unsolder the wires going to the L6 choke, remove the choke and the plate on which it is fixed (see Fig. 6) from the chassis. This will open access to the UHF installation and turn off the super-regenerator cascade. Turning off the super-regenerator is necessary so that its own oscillations do not interfere with the UHF tuning. To one of the extreme and middle terminals of the inductor L1 connect the output of the spectrum analyzer GKCH (or the output of the RF generator). The input of a spectrum analyzer or an oscilloscope is connected to the coupling coil L4. It should be recalled that the connection of devices to the elements of the receiver must be made with coaxial cables of a minimum length, cut on one side for soldering. The termination ends of these cables should be as short as possible and soldered directly to the terminals of the respective elements. It is strongly not recommended to use oscilloscope probes to connect devices, as is often done.

With a selection of capacitor C1, the UHF input circuit is tuned to a frequency of 90 MHz, and the output circuit by a selection of capacitor C4 is tuned to a frequency of 105 MHz. It is convenient to do this by temporarily replacing the corresponding capacitors with small-sized trimmers. If a spectrum analyzer is used, tuning is performed by observing the real frequency response on the analyzer screen (Fig. 13). If an RF generator and an oscilloscope are used, first adjust the input circuit, and then the output circuit according to the maximum signal amplitude on the oscilloscope screen. At the end of the tuning, it is necessary to carefully unsolder the tuning capacitors, measure their capacitance and select permanent capacitors with the same capacitance. Then you need to re-check the frequency response of the UHF cascade. On this, the establishment of the receiver can be considered complete. It is necessary to return it to its place and connect the L6 choke, check the operation of the receiver in the entire frequency range.

Rice. 13. Analyzer readings

The operation of the receiver is checked by connecting an antenna to the input (terminals XT1, XT2), and a loudspeaker to the output. Keep in mind that a super-regenerative detector can only receive FM signals on the slopes of its circuit's resonant curve, so there will be two settings per station.

If an authentic horn manufactured in the 20s of the last century is supposed to be used as a loudspeaker, it is connected to the output of the receiver through a step-up transformer with a voltage transformation ratio of about 10. You can do otherwise by including the horn capsule directly into the anode circuit of the VL6 lamp. This is how they were connected in receivers in the 20s and 30s. To do this, the output transformer T2 is removed and the terminals XT3 and XT4 are replaced with a 6 mm "Jack" socket. The desoldering of the socket and plug of the horn cord must be done in such a way that the anode current of the lamp, passing through the coils of the horn capsule, amplifies the magnetic field of its permanent magnet.

Drawings (in the author's version) of individual elements of the receiver can be downloaded from ftp://ftp.radio.ru/pub/2015/03/UKW.zip.

Author: O. Razin

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