RO4404 Triode Vacuum Tube

The RO4404 is the Visseaux / Televisso branding of the strict pre-war European 4 V directly heated low-power output triode (c. 1930), a confirmed sibling of the Philips-Miniwatt D404 / Telefunken RE604 / Tungsram P460 / TeKaDe 4K60 / Valvo LK460 family on the European 4-pin B4 base. RO4404 = P460 is documented by the Visseaux maker equivalence table itself — promoting RO4404 from third-party-table inference into the strict equivalence core. Three primary-source manufacturer datasheets agree on the same physical tube under different measurement conventions: TeKaDe 4K60 (RVF Roehrentaschenbuch M1, 1947) carries the single cleanest operating point in the whole family at Va = 250 V, Vg = −45 V, Ia = 40 mA, S = 2.5 mA/V, Ri = 1.4 kΩ, D = 29 % → μ = 3.45 (Ampera load-line calculator default); Philips / Miniwatt D404 (13/6/33) gives μ = 3.5, gm_norm = 2.7 mA/V, Ri_norm = 1.3 kΩ with a two-anchor table 250 V/−40 V = 40 mA and 200 V/−30 V = 30 mA; Telefunken RE604 publishes μ = 3.5, S ~ 3.5 mA/V at the same physical envelope. Single-ended Class A output at 250 V / 40 mA delivers about 1.7 W into 3.5 kΩ. SPICE status: model not bench-verified — fits are anchored on the well-documented D404 / RE604 / 4K60 maker data, and the pre-war wide-spaced geometry pushes the Koren EX exponent high (Philips / TFK variants at EX ≈ 1.95), so the model is accurate at and around the published operating points but should not be trusted for fine prediction far outside them or for Class A2 grid-current behaviour. The Visseaux 602 is treated as a probable mechanical / construction sibling (operator note: same construction and same plate as the RO4404), exposed in the SPICE deck as the provisional RO4404_602 alias pending a confirmed 602 datasheet. The E406 is NOT an equivalent (4 V / 1 A heater, μ ~ 6) and must never be swapped in via PX4-style adapters. Plate-dissipation ceiling held to the conservative 10 W family figure even though the Telefunken RE604 sheet permits 12 W.