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Where fixed and variable vacuum capacitors are used, what limits them in service, and how to specify a replacement without changing the tuning.
A vacuum dielectric gives a high voltage withstand in a small volume with very low loss, which is what a high power matching network needs. Where a ceramic part would need to be physically large to hold off the voltage, a vacuum capacitor does the same job in a package that fits inside a tuner.
Fixed capacitors set a value in the network. Variable capacitors allow the network to be tuned across a load range, which matters in plasma and industrial RF work where the load changes as the process runs. The two are not interchangeable, and substituting a fixed part for a variable one changes what the equipment can do.
The practical limits are voltage, RF current and mechanical wear on variable types. Bellows fatigue on a variable capacitor is a wear mechanism that no electrical test will show until it fails. Terminal heating is a sign that the RF current is above what the installation allows for.
Work from the series designation, the capacitance or capacitance range, the voltage rating and the mounting arrangement. In a matching network the physical dimensions matter too, because lead length and layout are part of the circuit at high frequencies.
Check the terminals for damage and, on variable types, operate the drive through its full range before installation. A part that has been through a long freight chain deserves five minutes of inspection before it goes into a system that is difficult to get back out of.
Matching network rebuilds usually happen at the same time as a tube change. Ordering the capacitor with the tube keeps both items on one delivery date.
Fixed and variable vacuum capacitors for RF matching networks and high power tuning circuits, quoted against the CKT series design
30 typesCCG series high voltage ceramic capacitors, water cooled and air cooled, for induction heating plant, RF generators and transmitte
Not without redesigning the network. The variable part exists so the circuit can be tuned to a changing load.
The series designation, the value or range, the voltage rating and the mounting arrangement.
Send the designations you have identified together with quantities. Price and availability come back by email.