4G25

The 4G25 is a TeKaDe vacuum rectifier with a directly heated 4 V, 0.3 A filament and a European four-pin B4 base, according to the data preserved in our sources. Its use in receiver power supplies is also documented in an Arlt collection of circuits and parts lists, which includes it among the rectifiers suitable for its projects.

On pages 37–39, the collection describes a single-tuned-circuit AC receiver using an EL-ES-Ferrokart coil or a conventional cage coil. The circuit uses REN904 and RES164 valves, plus an RGN354 rectifier; the parts list includes TKD 4G25 among the alternatives for the latter position. Interestingly, the heading calls it a ‘two-valve’ receiver despite showing a rectifier as well: the two valves in the title are those in the signal path, while the power supply adds its own valve.

The 4G25 also appears on page 36 in the parts list for ‘Dein Super’, a different project with AK2, a 904-family detector valve and a 164-family output valve. Here the rectifier entry again specifies 354 or TKD 4G25. Both applications illustrate this valve's role in home-construction projects; the circuit component values nevertheless apply to those projects and are not general 4G25 limits.

P. H. Brans's 1950 Vade-Mecum, on page 122, associates TeKaDe 4G25 with Philips 1802 and specifies a 4 V filament for both. This comparison supplements its bibliographic identification without establishing a maximum rectified current by itself. In particular, the number 25 in the designation is not treated here as a 25 mA rating: assigning a limit requires an explicit technical specification.