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The 1821 is a Philips full wave rectifier on a B4 base with a brown composition base. The UU5 is given as an equivalent but has twice the rating, so the UU5 may replace the 1821 but not the other way round.

Unlike our other examples of this Type this one is 23 mm shorter and a diameter some 6 mm smaller. The suggestion is that this is a later product - possibly post war.

See 1821 for internal details.

although the envelope is largely opaque, it can be seen that the height has been reduced by bending the pinch supports down.

The dome carries the identification. As it was made in England this was a product of a Mullard factory.

The balloon envelope is 46 mm in diameter and, excluding the B4 base pins, is 92 mm tall.

Reference: ¹⁰⁴³. Type 1821 was first introduced in 1930. See also 1930 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶