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The U18/20 is a medium power full wave rectifier. We have two Marconi examples in the collection. This version is in a longer and narrower envelope than U18/20 but despite different anode construction and envelope size the electrodes are the same size.

To protect the cathode from damage the rectifier needs to be fed from a supply with an effective series resistance of 180 Ohms. The reservoir capacitor may have a maximum value of 16 μF

The classic envelope is 46 mm in diameter and, excluding the B4 base pins, is 124 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type U18/20 was first introduced in 1939.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.