RE504

The RE504 is a Telefunken triode intended for the final audio-frequency stage and for driving a loudspeaker. The manufacturer's technical sheet, on page 35, expressly presents it as a valve for this purpose and for heating the filament from a 4 V accumulator. Its role is therefore that of the last audio amplification stage, as the original description of a ‘loudspeaker valve’ itself indicates.

One detail that requires careful reading is the distinction between the accumulator and the filament: the document mentions a 4 V accumulator, but specifies 3.5 V and a current of 0.50 A for the filament. The two figures describe different parts of the supply and should not be treated as two interchangeable nominal filament voltages. The sheet also specifies a heating regulator of at least 5 Ω: this figure concerns supply regulation, not the filament resistance.

For the anode circuit, Telefunken lists voltages from 80 to 220 V and an average anode current of 15 mA. The negative grid bias must be selected according to the anode voltage: the text gives values from −5 to −14 V. A transconductance of 0.8 mA/V and an internal resistance of 6000 Ω are also listed. The manufacturer states that all the figures are approximate; the average current must therefore not be mistaken for a maximum rating, nor should the data collected in the table be regarded as a single operating point. The sheet's curves separately show the behaviour at anode voltages of 100 and 200 V.

The documentation also preserves a useful detail for identifying the versions: the RE504 with a European base is described as formerly designated RE209, while the RE504t with a Telefunken base is described as formerly designated RE97. The final letter thus distinguishes two versions with different bases, shown on the same sheet. This information makes it possible to interpret the old designations without confusing the two versions; the document consulted does not, however, establish a precise date for the change of designation.