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Radio Valve Type 5Z4G, Britain, Mid 20th Century

Inventory Number: 48685

Number of documents: 1

Document Type: Miscellaneous Note

Document Heading: Technical Details


The 5Z4G is a full wave rectifier. Professional equipment, including radar etc., sometimes required circuits in which valve cathodes carried large signals and had to 'float' at voltages well below that of the chassis. Glass-envelope '-G' versions of common types were therefore required. The metal envelope valves had to have the outer envelope at below cathode potential to prevent them acting as an anode so were at a disadvantage. Initially, these '-G' versions were larger than their metal counterparts but with the introduction of 'pinchless', slimline '-GT' types 5Z4GT the advantage of the compact metal types was reduced to the point where RCA decided to phase out production in favour of (slightly cheaper) all-glass types. Type 5Z4 was indirectly heated and although heater and cathode were internally connected, the heater-cathode insulation was deliberately thickened so that the rectifier's cathode heated slightly more slowly than the other valves, thus eliminating HT voltage surges. Designed to supply equipment of up to 40 Watts total power, this rectifier was made by several manufacturers. This suggests a very popular type, and one that found use in military equipment during WW2.

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