in paper and metal
One of my young friend the chemist was necessary a variable capacitor (KPE) and it was found that find it not so simple, in connection with which he had the idea to do it yourself. At first I It seemed that the topic is not worth a damn - and ready to KPE in bulk, and easy familiarity with the technical description makes it obvious inappropriateness of independent manufacturing ... But, sending it into Google, just in, he decided to go look, and found that KPE is now really very little in the sale, and prices are available unhealthy, and most importantly - there is absolutely no information on how to actually arranged this simple RADIODETAL, resulting in (after getting acquainted with an extremely simple principle of work and patterns of school physics textbook for the penultimate year) and there is the idea that "here we are right now with his right foot to the left ear!" :)
therefore took the trouble to describe in detail the actual concrete radioelement with an explanation that there is reason, and decided to throw a compilation of letters and journal - As example of the difference between the concept drawings in the textbooks and the actual radio components, which can indeed be practically used.
For example KPE unit is taken from domestic broadcast receivers III-class (and not just any military or special applications, which are arranged much more difficult), ie the most that neither is mediocre:). Currently, the receivers KPE as an element of adjustment, of course, hardly used - it replaced by a reverse pn-junction varactors - special diode capacitance are highly dependent on the applied reverse bias to them, but in general number of applications, in particular in the differential dielkometre (device for measuring the dielectric constant), for which proper and needed KPE my friend, the air variable capacitor irreplaceable ...
(clickable images)
housing block cast of silumin (an alloy of aluminum and silicon, the basis for the choice of material - easy handling, precision casting and strength with sufficient rigidity) and electrically associated with moving plates - the rotor. On the advantages of such a connection is compared with the design, where the body is connected to the stator plates later. stator plates are made of aluminum (high electrical conductivity and corrosion resistance, and lightness) and connected to the perforated bags plates, the holes are laminated tabs plates. Double lining and made of tin (tinned) copper, since each unit stator is fixed in the body by soldering, and brazing aluminum directly is extremely difficult, ie, besides separator functions, they play the role of carriers. Three-piece unit, and each package is isolated from the stator housing and the other two set to porcelain (the best insulator, is not hygroscopic and provides minimal losses, practically eternal) columns, with one end pressed into the case, but on the other end of each of them pressed on a copper tinned Cap for fastening the package plate by soldering. One of the caps on each section has a silver-plated tab with a hole for soldering output.
Plates rotor is also made of aluminum and pressed on for the bronze (copper-tin alloy; need high strength, stiffness, corrosion resistance and low coefficient of friction in pair with steel, since the shaft is part of ball bearings it) shaft that is common to all three sections. Press-on plate on the shaft provides sufficient rigidity of the rotor, but the ends of rotor plates are no protected and may be subject to external distorting, so They recorded a perforated steel plate. The latter is also a mechanical stop at Pushing movable plates in fixed, ie by careless typing subjected to additional, "remove" it from the mechanical impact of plates, so besides expanding, projections plates are made longer and more curved. In order to make the moment of total input of moving plates fixed to avoid their closure plate, under the latest More getinaksovaya is enclosed insulating gasket. To protect against corrosion points of contact of aluminum with steel plates (two disparate metal in a damp environment form a galvanic cell, and therefore heavily corroded), the latter are covered with paint. In carrying tin lining is tread pair of copper-aluminum (see school textbook Chemistry in the penultimate class), so there is no need to defend. The ends of each plate package as a result of exposure to the deforming mechanical impact, have radial slits to facilitate subsequent edits.
addition to the capacitor plates, pressed on the shaft and the slotted silver-plated discs, providing a sliding contact - each section of his own. Fixed contact is provided with brass (copper-zinc alloy; need resilience and durability with good electrical conductivity), silver-plated brushes are also equipped with paddles for soldering wires. As the touching point of rolling contact in this case fundamental importance (unlike potentiometers) brush for the contact reliability made double. Each brush is attached to the body of a brass caps (as compared with the rivet connection is more rigid and provides a fixed position relative to the body brush). Because the rotor is electrically common to all three sections, triple contact double brushes provides a guaranteed connection with any rotor position for a long time. Individual withdrawal from the mobile contact of each section is convenient because it allows each of them to connect their own shielded twisted pair to the desired location of the scheme (they are usually physically separated).
rotor shaft to ensure a smooth and proportionality of the force of the governing body rotates in the two ball bearings. To ensure minimum axial play, the bearing is made asymmetric. Front entrance bearing is a radial-thrust and is is pressed into a steel casing with a hemispherical cup of the working surface on which the rolling steel balls. The role of the second ring front bearing performs calibrated facet of the rotor shaft. Rear bearing is stubborn and is the only steel ball, rotating between a hemispherical recess in the shaft end and a conical recess in the steel propeller thrust bearing provided with a slot for a screwdriver and nut, which allows after selecting a backlash to fix the desired position.
On the front end of a shaft mounted driven gear reducer, physically representing two connected steel spring duralumin (copper-aluminum alloy; need ease with high strength and durability) gears, one of which is rigidly mounted on a steel shaft with a retaining screw, and the other is free to rotate on it as the axis, is prevented from axial displacement split washer vnatyag worn on the ring groove at the end of the shaft. In general, such a design driven gear has two objectives: to make the gear backlash-free connection (contractible spring two halves of the driven gear their teeth tightly grasping each tooth lead, thereby ensuring the absence of a dead zone when the direction of rotation) and adjustable limit the capacitance due to changes in the maximum depth input moving plates fixed, which is provided in the body milled gears semi-circular groove and falling into his finger steel hull reducer. In this design by changing the relative position of the halves driven gear can change the depth of the input in the range of 0-30 degrees (at full during 180 degrees).
pinion gear reducer is made of thermosetting plastics (phenol-formaldehyde, provides the necessary rigidity, wear resistance and durability) and has two pulley: a smaller diameter - the actual driving, which wrapped nylon fishing line, rope or cord, connects gear with body control, and more - an indicator that provides pointer movement scale. Since the drive pulley should provide clearly commit extreme positions, in which he experiences a significant mechanical loads, it contains within itself the pin on which to put on two end loop connection with the control stick to prevent slippage which at its end is the hat.
drive the same pointer is a passive device, it is closed loop, allows sliding and therefore is fixed on a pulley rope threading between two curly projections, similar mooring bollard. Pinion gear rotates on a steel axle having a slot at the end of a screwdriver and fixed front slotted the puck planted in the designated for her recess at the end of the axis. The second end of the shaft has a bearing surface and a threaded shank of smaller diameter, fastened through the foramen ovale to the steel gear housing nut and washer. Foramen ovale allows you to adjust the depth of engagement gear reducer, and adjust it to the extent of wear. In addition, the foramen ovale allows it to adjust the upper limit of the capacitance by changing the relative position of two parts driven gears without the need to dismantle the leadership (and hence accompanied his dismantling of the system and ropes). On the other hand, Use a slotted axle instead of screws and split lock washers as a limiter allows to disassemble the pulley, not having access to the rear side of the gear housing.
Overall unit is mounted in the construction of screws passed through three holes in the steel legs, two of which are located on the gearbox housing and one - an extra steel leg, attached to the rear of the unit capacitors with two screws: conventional and eccentric, allows to some extent change the position of the pulleys relative to the plane of the drive ropes, providing them with a smooth winding of the pulleys (the overlap - Is a step in the adjustment, which is often not possible). All three mounting holes with rubber shock absorbers to prevent mechanical modulation of the rotor vibration device.
bearing block, sliding contacts, gears and axle pulley lubricated with grease grease.
should be noted that this instance of KPE unit, with advanced age (released in August 1959) and having worked on a daily basis for over 30 years now Time is fully functional, absolutely no backlash, lightweight and mobile. Even the rubber shock absorbers have no cracks are fresh and springy as a \u0026lt;a metaphor>. There is no doubt that he can and has to serve for fifty years, so The popular expression "did for centuries" is not always hyperbolic:))
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