The LP4 is Ferranti's version of the PX4, one of the classic audio power triode valves. We believe, however, that this exhibit is in fact a rebranded Marconi Osram PX4.

Ferranti did manufacture some of there own valves during the later 1930s but their 'home-brewed' LP4s were bulbous and stumpy. After WWII Ferranti's tended to buy in and re-label other manufacturers' valves; this is one of them.

The valve in the photo has blackened fins spot-welded to a shiny anode. This shows that it is of post-1938 manufacture and has been uprated from 250 V and 12 Watt dissipation to 300 V and 15 Watt dissipation. From around 1950 the fins were omitted but the outer surface of the anode was given a grey coating instead.

The classic envelope is 48 mm in diameter and, excluding the B4 base pins, is 120 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type LP4 was first introduced in 1933. See also 1933 adverts.

Pin Connections

B4

1

2

3

4

a

g1

f

f