Typical GTVAC variable ceramic vacuum capacitors. Two sets of concentric cylinders,one on a sliding shaft, The other fixed, are enclosed in an evacuated ceramic envelope with OFHC copper seals located at both ends. A flexible metal bellows, attached to a sleeve type bearing, maintains the vacuum while allowing the capacitance to varied. Extremely low losses occur in vacuum capacitors because of the ceramic envelop and vacuum dielectric, The types of capacitors offer such features as high withstand voltage, small size, good Quality factor, stable and reliable properties. Theyare widely used as tuning components in HF and HV equipment for communication broadcasting sets. The vacuum capacitors have beenapproved and accepted by Jennings and users.