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Vacuum-Variable-Capacitors-Jennings-Datasheets.pdf
Jennings variable vacuum capacitor. Two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic.
Source: www.amstechnologies-webshop.com
Date Published: 4/26/2022
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vacuum variable capacitor products for sale – eBay
JENNINGS VACUUM VARIABLE CAPACITOR CADB-15-20N77 ANTENNA TUNER HAM. $75.00. $9.50 shipping ; Jennings UCS-500 Variable Vacuum Capacitor 15KV 500pf. $199.00.
Source: www.ebay.com
Date Published: 5/28/2021
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— Jennings® Vacuum devices – ABB
Jennings variable vacuum capacitor. Two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic.
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Date Published: 8/25/2021
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201 to 500 pf Max – Vacuum Variable – Capacitors – RF Parts
201 to 500 pf Max ; CV1C-500UIHN/15 Vacuum Variable Capacitor, 12-500pf, 15kv Peak / 9KV, Comet (NOS). $899.95 ; UCS300-10KV Jennings Vacuum …
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Date Published: 5/12/2021
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Vacuum Capacitors: 101 – 500pF – Surplus & Sales of Nebraska
Jennings vacuum variable capacitor. 75 amps. 1/2″ shaft. Front head is tapped and has sol copper block attached (removable). Rear (fixed end) has a …
Source: www.surplussales.com
Date Published: 11/14/2021
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- Author: Brighton Beach
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- Date Published: 2021. 12. 25.
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What does a vacuum variable capacitor do?
A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating than an air dielectric using a smaller total volume.
What is the difference between capacitor and variable capacitor?
The variable capacitors are the ones whose capacitance value can altered either electrically or mechanically. The variable capacitors consist of sets of stationary and movable plates. A shaft is attached with the movable plates and by rotating the shaft, the capacitance value can be altered.
What are the two types of variable capacitor?
There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.
Where is a variable capacitor used?
Variable air capacitors are used in circumstances where the capacitance needs to be varied. They are sometimes used in resonant circuits, such as radio tuners, frequency mixers or antenna impedance matching applications. Another use for variable capacitors is while prototyping an electronic circuit design.
How does a variable capacitor work?
Unlike standard fixed capacitors, variable capacitors are configured to allow changing capacitance levels. In most cases, variable capacitance is accomplished by altering the distance between the parallel plates in a capacitor or by shifting the cross-sectional area at which the plates face one another.
How many types of variable capacitors are there?
What are the two types of variable capacitors? They are tuning capacitors and trimming capacitors.
How do I choose the right capacitor?
The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V). So, the capacitor voltage rating should be 226.67V (170/0.75).
What is the working voltage of a variable capacitor?
Voltage rating, capacitance range, polarity
Trimmer capacitors can be rated for voltages up to 300 volts, although voltage ratings of up to 100 volts are much more common. Since trim caps are variable capacitors, they come in a capacitance range rather than a single capacitance value.
How do you identify capacitor types?
Generally the first two digits indicate the capacitors value and the third digit indicates the number of zero’s to be added. For example, a ceramic disc capacitor with the markings 103 would indicate 10 and 3 zero’s in pico-farads which is equivalent to 10,000 pF or 10nF.
Does the type of capacitor matter?
Yes, the type of capacitor can matter. Different types of capacitor have different properties. Some of the properties that vary between capacitor types: Polarised vs unpolarised.
What is the symbol of a variable capacitor?
The arrow symbol indicates a variable capacitor (adjustable by the equipment user, and the T shaped diagonal indicates a preset capacitor, for technician adjustment only. The dotted line connecting a pair of variable capacitors indicates that they are ganged.
What are plastic capacitors used for?
Film capacitors are also known as plastic film capacitors or film dielectric capacitors. Plastic film capacitors are mainly used in circuits where low loss and high insulation resistance is required.
What is the use of non polarized capacitor?
A non-polarized capacitor is a type of capacitor that has no implicit polarity – it can be connected either way in a circuit. They are mainly used in circuits of coupling, decoupling, feedback, compensation, and oscillation.
How do you find the capacitance of a capacitor?
The capacitance of a capacitor is the ability of a capacitor to store an electric charge per unit of voltage across its plates of a capacitor. Capacitance is found by dividing electric charge with voltage by the formula C=Q/V.
Is a type of capacitor that has no implicit polarity it can be connected either way in a circuit?
A non-polarized (“non polar”) capacitor is a type of capacitor that has no implicit polarity — it can be connected either way in a circuit. Ceramic, mica and some electrolytic capacitors are non-polarized.
201 to 500 pf Max
$299.95
Out of stock
CVDE-200-5 Jennings 15-250pF 5Kv Variable Vacuum Capacitor
Used, Great Condition * No longer available for export
Made in the USA by Jennings
SKU: CVDE-200-5
Please see our Warranty page regarding our warranty.
Made in the USA
Jennings Vacuum Capacitors
Jennings Vacuum Capacitors
A vacuum capacitor is a capacitor which uses vacuum as dielectric instead of air or other insulating materials. The vacuum dielectric allows a higher voltage rating that an air dielectric.
Jennings Vacuum capacitors
A typical Jennings vacuum capacitor consists of two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic envelope with OFHC copper seals at both ends. A flexible metal bellows, attached to a sleeve-type bearing, maintains vacuum while allowing capacitance to vary.
The linear sliding motion required to vary capacitance is converted to rotary tuning via an adjustment screw; in many capacitors, direct pull tuning is an alternative. Internal breakdown voltage is primarily determined by the spacing of the opposing plates and a high vacuum level.
The following are general specifications pertaining to Jennings vacuum capacitors. Current ratings are for normal convection cooling in ambient temperature of 25 °C unless otherwise specified.
Maximum allowable operating temperature — 125 °C (257 °F) for ceramic capacitor
Cooling — natural convection unless otherwise specified
Mounting position — any
Rotation to increase capacity — counterclockwise
If none of our standard catalog models meet your needs, our engineers will work with you to design a custom solution to meet your specific needs.
Features
Vacuum variable capacitor
A vacuum variable capacitor
A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating than an air dielectric[1] using a smaller total volume. However, many dielectrics have higher breakdown field strengths than vacuum: 60-170 MV/m for teflon, 470-670 MV/m for fused silica and 2000 MV/m for diamond, compared with 20-40 MV/m for vacuum. There are several different designs in vacuum variables. The most common form is inter-meshed concentric cylinders, which are contained within a glass or ceramic vacuum envelope, similar to an electron tube. A metal bellows is used to maintain a vacuum seal while allowing positional control for the moving parts of the capacitor.[2]
Invention [ edit ]
Nikola Tesla filed a patent in 1896 for a vacuum capacitor. The original use was to enhance the quality of the electrical components for handling “currents of high frequency and potential”. These components were necessary for the DC impulse research which Tesla was studying. Commercial products have been available since 1942.[1]
Applications [ edit ]
Vacuum variable capacitors are commonly used in high-voltage applications: 5000 volts (5 kV) and above. They are used in equipment such as high-powered broadcast transmitters, amateur radio RF amplifiers and large antenna tuners. Industrially they are used in plasma generating equipment, for dielectric heating, and in semiconductor manufacturing.[1] The main applications today are RF plasmas of 2 to 160 MHz where the vacuum capacitor is used as the impedance variation part in an automatic matching network in the fabrication of chips and flat panel displays.
A 12 pF 20 kV fixed vacuum capacitor
Other variations of vacuum capacitors include fixed-value capacitors, which are designed very much like the variable versions with the exception that the adjustment mechanism is omitted.
Comparison [ edit ]
When compared to other variable capacitors, vacuum variables tend to be more precise and more stable. This is due to the vacuum itself. Because of the sealed chamber, the dielectric constant remains the same over a wider range of operating conditions. With air variable capacitors, the air moving around the plates may change the value slightly; often it is not much but in some applications it is enough to cause undesirable effects.[citation needed]
Vacuum variable capacitors are generally more expensive than air variable capacitors. This is primarily due to their design and the materials used. Although most use copper and glass, some may use other materials such as ceramics and metals such as gold and silver. Vacuum variables also vary in adjustment mechanisms.
Capacitor Types: Fixed & Variable Capacitors
Capacitor Types: Fixed & Variable Capacitors
Capacitors can be classified depending upon their fixed or variable capacitance as follows −
Fixed Capacitors
Those capacitors whose value of capacitance is fixed during the manufacturing and cannot be changed later are known as fixed capacitors. The symbol of the fixed capacitor is shown in figure.
The fixed capacitors are classified into two categories as −
Polarized Capacitors
Non-Polarized Capacitors
Polarized Capacitors
Those capacitors which are having the specified positive and negative polarities, are called as polarized capacitors. When these capacitors are used in the circuits, they should be connected in perfect polarities.
Polarized capacitors are further classified as −
Electrolytic Capacitors
Those capacitors in which some electrolyte is used as a dielectric medium are called as electrolytic capacitors. These are the polarised capacitors i.e. marked with specific polarities as anode (+) and cathode (-). There are mainly three types of electrolytic capacitors −
Aluminium Electrolytic Capacitor
In these capacitors, the anode (+) terminal is made of a pure aluminium foil with an etched surface. The aluminium forms a thin insulating layer of aluminium oxide that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer and acts as the cathode (-) terminal of the capacitor.
Tantalum Electrolytic Capacitor
It consists of a pellet of porous tantalum metal that acts as the anode of the capacitor. The tantalum metal is covered by an insulating oxide layer that forms the dielectric and surrounded by a solid or liquid electrolyte that acts as cathode terminal.
Niobium / Niobium Oxide Electrolytic Capacitor
In a niobium capacitor, the anode terminal is made of passivated niobium metal on which an insulating niobium pent-oxide layer acts as the dielectric. A solid electrolyte on the surface of the oxide layer acts as the cathode of the capacitor.
Super Capacitors
These are the types of capacitors whose capacitance value is much greater and they can store and deliver charge much faster than the other types of capacitors. As these capacitors are also polarized capacitors, therefore they are also having specific positive and negative polarities.
The types of super capacitors are as follows:
Double Layer Capacitor
It is an electrostatic capacitor. The principle of this capacitor is based on the double-layer capacitance. In an electrical double layer which appears at the interface between a conductive electrode and a liquid electrolyte. Two layers of charge with opposite polarity form at this interface, one at the surface of electrode and one in the electrolyte. These two layers are separated by a single layer of solvent molecules that stick to the surface of electrode and act as dielectric in the capacitor.
Pseudo Capacitor
The charge in the pseudo capacitor is stored faradically by the transfer of charge between electrode and electrolyte. The pseudo capacitor is a part of an electrochemical capacitor.
Hybrid Capacitor
These capacitors are the combination of double layer capacitor and pseudo capacitor. In these super capacitors, the anode is made of pre doped carbon and the cathode is of activated carbon. The lithium-ion capacitor is an example of hybrid capacitor.
Non-Polarized Capacitors
The non-polarised capacitors are the ones that does not have specific positive and negative polarities i.e. they can be connected in the circuits without considering that which lead is connected to the positive and which one to the negative. There are various types of nonpolarized capacitors as follows −
Ceramic Capacitors
When the ceramic material is used as a dielectric medium in the capacitor, the capacitor is called as ceramic capacitor.
Film Capacitors
These types of capacitors have a film substance as a dielectric medium. They are of following types −
Paper Capacitor
The dielectric medium used in paper capacitors is a waxed or oiled paper. The paper is sandwiched in between two thin tin foils sheets and these sheets are rolled into a cylindrical shape and encapsulated in a plastic enclosure.
Metal Film Capacitor
In these capacitors, a paper coated with metallic film is used as a dielectric medium. The metal (aluminium) coated sheets are rolled in the form of cylinder and encapsulated in a plastic enclosure.
Miscellaneous Capacitors
There are some more capacitors which are named according to dielectric material used. Some of them are −
Mica Capacitor
These capacitors consist of a thin mica sheet as dielectric. In these capacitors, a mica sheet is sandwiched in between thin metal sheets, leads are taken out and this whole assembly is enclosed in a plastic enclosure.
Glass Capacitor
In these capacitors, the glass is used as the dielectric medium. These are noise free capacitors with the low temperature coefficient.
Air Capacitor
When air is used as the dielectric medium in the capacitor, the capacitor is known as an air capacitor.
Vacuum Capacitor
In these capacitors, vacuum is used as a dielectric medium.
Variable Capacitors
The variable capacitors are the ones whose capacitance value can altered either electrically or mechanically. The variable capacitors consist of sets of stationary and movable plates. A shaft is attached with the movable plates and by rotating the shaft, the capacitance value can be altered.
There are mainly two types of variable capacitors −
Tuning Capacitors
The tuning capacitors are type of variable capacitor consisting of a set of semi-circular stationary (stator) and movable (rotor) plates, a shaft is attached to the movable plates, and this whole assembly is supported by a frame. The movable plates when moved into the space between the stator plates, they come close to form plates a capacitor. When the movable plates sit completely in between the stator plates, the capacitance value being maximum and when the movable plates are completely out of stator, the capacitance value is minimum.
Trimmer Capacitors
The capacitance of a trimmer capacitor is varied by using a screwdriver. These capacitors consist of two plates: one is stationary and the other is movable and these plates are arranged parallel to each other with a dielectric material in middle.
These capacitors have three terminal leads: one is connected to stationary plate; second is connected to movable plate and the third lead is common. The variation of capacitance value can be observed with the movement of semi-circular shaped movable disc. Trimmer capacitors are frequently arranged on the printed circuit boards so that the user does not have the right of entry to change them.
Depending upon the type of dielectric material used, these types of capacitors are classified into two types −
Air trimmer capacitor
Ceramic trimmer capacitor
Basic Electronics – Variable Capacitors
Basic Electronics – Variable Capacitors
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There are many types of capacitors depending upon their function, the dielectric material used, their shape etc. The main classification is done according to fixed and variable capacitors.
Types of Capacitors
The classification is as shown in the following figure.
The main classification is just like the above one. The fixed capacitors are the ones whose value is fixed at the time of manufacturing itself and the variable ones provide us with an option to vary the value of capacitance.
Variable Capacitors
Let us know something about the variable capacitors whose value alters when you vary, either electrically or mechanically. Variable capacitors in general consists of interwoven sets of metallic plates in which one is fixed and the other is variable. These capacitors provide the capacitance values so as to vary between 10 to 500pF.
The ganged capacitor shown here is a combination of two capacitors connected together. A single shaft is used to rotate the variable ends of these capacitors which are combined as one. The dotted line indicates that they are connected internally.
There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.
Tuning Capacitors
Tuning capacitors are popular type of variable capacitors. They contain a stator, a rotor, a frame to support the stator and a mica capacitor. The constructional details of a tuning capacitor are shown in the following figure.
The stator is a stationary part and rotor rotates by the movement of a movable shaft. The rotor plates when moved into the slots of stator, they come close to form plates of a capacitor. When the rotor plates sit completely in the slots of the stator then the capacitance value is maximum and when they don’t, the capacitance value is minimum.
The above figure shows a ganged tuning capacitor having two tuning capacitors connected in a gang. This is how a tuning capacitor works. These capacitors generally have capacitance values from few Pico Farads to few tens of Pico Farads. These are mostly used in LC circuits in radio receivers. These are also called as Tuning Condensers.
Trimmer Capacitors
Trimmer capacitors are varied using a screwdriver. Trimmer capacitors are usually fixed in such a place where there is no need to change the value of capacitance, once fixed.
There are three leads of a trimmer capacitor, one connected to stationary plate, one to rotary and the other one is common. The movable disc is a semi-circular shaped one. A trimmer capacitor would look like the ones in the following figure.
There are two parallel conducting plates present with a dielectric in the middle. Depending upon this dielectric used, there are air trimmer capacitors and ceramic trimmer capacitors. The constructional details of a trimmer capacitor are as shown below.
One of the two plates is movable, while the other is fixed. The dielectric material is fixed. When the movable plate is moved, opposite to the area between movable and fixed electrode, then the capacitance can be changed. The capacitance will be higher if the opposite area gets bigger, as both the electrodes act as two plates of a capacitor.
The Trimmer Capacitors are easily fixed on a PCB (Printed Circuit Board) and they are mostly used for calibration of equipment.
Capacitors for Sale
Capacitors for Sale
Jennings Vacuum Variable This is a Jennings model CVDB 1500 15N25 vacuum variable. It’s 36 through 1500 pF at 15,000 VDC. I measured one and at the low end, it measured 30 pF. I’m using this one for my own HF antenna tuner. It may have a small dent but the vacuum has not been broken. I have 1 of these left removed from Collins 208U linear amplifiers. I also have a 2-phase servo to drive the capacitor electromechanically. See these listed on the Miscellaneous page.
Jennings Vacuum Variable This is a Jennings model CVDP 2300-15S vacuum variable. It’s 50 through 2300 pF at 15,000 VDC. It will handle at least 100 Amps RMS up through 100 MHz and 200 Amps at 2 MHz. I have 1 of these big boys left, removed from Collins 208U linear amplifiers. I also have a 2-phase servos to drive the capacitor electromechanically. See these listed on the Miscellaneous page. There may be an inconsequential dent or two on the body.
Resonant Tank This parallel resonant tank is from a Collins CU-1464 antenna tuner. The range of resonance is 6.5 MHz through 8.5 MHz. The Jennings vacuum variable capacitor model UMF-800 is rated at 18,000 VDC and is 12 pF through 800 pF.
High Voltage RF Plate Coupling Cap This is a 2000 pF, 10,000 VDC coupling capacitor. It has very low inductance, and can carry 100 Amps of RF at all HF frequencies.
High Voltage RF Bypass Circuit There are 2000 pF low-inductance bypass capacitors at the ends of a choke which traverses the middle of the tube. This capacitor/inductor unit passes 7500 VDC from the lower compartment, through the RF deck to the anode compartment. The top end then is connected to the plate voltage supply choke (listed under Inductors) which is directly connected to the tetrode’s anode.
Jennings Vacuum Variable A nice variable for that antenna tuner, or for use in a pi network on the plate of that new linear you’re thinking of building…
Jennings Vacuum Variable This variable has the hardware to operate the capacitor already installed. Simply rotate that gear on the end, and the cap traverses its range with mechanical stops built in.
Resonant Tank A tank circuit with a variable inductor and air dielectric variable capacitor. The circuit resonates from 1.8 MHz through 32 MHz and was in the plate circuit of a driver for the grid of a 4CX10000D linear.
Large Electrolytic This is a large aluminum electrolytic rated as 12,000 uF at 250 VDC. I have several, so series a few to get up into the kilovolt range with lots of Joules.
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