E406N

The E406N is a directly heated Philips Miniwatt output triode, listed in the original Miniwatt-Lampen 1936–1937 catalogue among 4 V output-stage valves. Its application code is 12, defined by the catalogue legend as output amplifier. The retained photograph shows a Philips Miniwatt E406N specimen with a shaped glass envelope and European four-pin base. The catalogue date documents its presence in that range, without necessarily being its introduction year.

The filament requires 4 V at about 1 A and is itself the emitting surface, without a separately heated cathode. The catalogue names the base A40 with connection diagram 1. The diagram, explicitly a bottom view, shows two filament contacts, one grid and one anode. The table gives dimensions of 135 × 60 mm, with a note excluding pins. These are the dimensions in that edition, not necessarily those of another construction or a modern similarly named equivalent.

The Philips row gives 250 V maximum anode voltage, 48 mA anode current and about −22 V grid bias. It lists normal transconductance 3.5 mA/V, amplification factor 6, normal internal resistance 1700 Ω and cathode resistor 460 Ω. Maximum anode dissipation is 12 W, while useful output is listed as 1.75 W at 10% harmonic distortion. These powers mean different things: allowable anode heat versus output under catalogue conditions. The optimum-load box is empty; it cannot be completed from a merely similar triode.

The initial letter offers a useful curiosity for reading old diagrams. Later pages explain the newer Miniwatt designation system, in which E identifies a 6.3 V car-radio series, but explicitly preserve the names of types designated under the previous system. E406N is indeed in the 4 V table. Mechanically applying the newer legend to its name would therefore give the wrong supply. The correct value comes from the specific manufacturer row read with its legend and base diagram.