Virtual Valve Museum

Virtual Valve Museum

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CV291 mixer diode ("crystal valve")

Size This "valve" measures 20x7mm overall (~6mm across the main body)


Frequency of operation 6000MHz
Min back to forward resistance ratio 8:1
Min forward resistance 265 ohms
Max amount by which performance is below "standard best" 3.0db
Max noise temperature ratio 2.6
Nominal IF impedance 350 ohms


The foil wrapping is designed to protect it from damage caused by RF fields.

Crystal valves were used in the mixers of radar receivers and were susceptible to burn-out caused by the high RF power of the transmitted pulse. It was for this reason that TR Cells were so vital in single-aerial operation, and also the reason for the development of thermionic diode mixers such as the CV58 and CV258.

(Note: Yes I know it is a semiconductor, but as these crystal valves were so vital to radar and many of my other unusual valves are for radar too, surely this deserves to be an 'honorary valve'!)


CV291 foil wrapped