Same B4 base and ~7 V heater DHT triode, listed as similar with differences — pin functions require verification before substitution
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Anodenspannung max800V
Anode Dissipation (max)Anodenbelastung max32W
Typical Operating
Anode Voltage (typical)Anodenspannung (typical)440V
Grid 1 Bias VoltageGittervorspannung-19V
Anode ResistanceAnode Resistance (derived)3,500Ω
TransconductanceSteilheit2mA/V
Amplification Factor (μ)Verstärkungsfaktor
Output
Output PowerWechselstromleistung max8.5W
Heater
Heater VoltageFadenspannung7V
Heater CurrentHeizstrom1.1A
Notes
The Telefunken datasheet explicitly states: 'RV 258 und RV 218 unterscheiden sich in ihren Konstanten nicht (abgesehen von den Belastungsdaten)' — the electrical constants (mu, gm, ra) are identical to the RV218; only the maximum ratings differ.
RV258 supersedes RV218 for all applications where Va >440 V or Pa >24 W. It is a direct pin-for-pin replacement using the same B4 socket wiring (Sockelanordnung Nr. 1).
Filament voltage stated as 7.0 V in this datasheet; the RV218 datasheet (same Telefunken book, adjacent page) states 7.5 V. Reference indexes list 7.2 V. The discrepancy likely reflects rounding — both tubes operate from the same nominal ~7 V filament supply.
The RV258 has a brown matte anode, distinguishing it visually from the RV218.
High efficiency at high anode voltages is achieved via optimum load matching (ratio ~1:3 to 1:4), enabling 8.5 W audio output at Va=800 V, Pa_max=32 W.
Same warnings as RV218 apply: risk of UHF self-oscillation when paralleling tubes; special grid construction prevents Durchstoßen (grid-emission breakthrough).
Amplification factor mu = 1/D = 1/0.14 ≈ 7; anode resistance ra derived as mu/gm = 7/0.002 = 3500 Ω (not explicitly stated in datasheet).
Codewort (factory test code): nsypa.
Pin Layout — B4
1Filament (+)
2Anode
3Control Grid
4Filament (−)
Socket-Compatible Tubes ⚠ Not electrically compatible