Same B4 base and 7.2V heater DHT triode, listed as similar with differences — pin functions require verification before substitution
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Anodenspannung max440V
Anode Dissipation (max)Anodenbelastung max24W
Typical Operating
Anode Voltage (typical)Anodenspannung (typical)350V
Grid 1 Bias VoltageGittervorspannung-19V
Anode ResistanceAnode Resistance (derived)3,500Ω
TransconductanceSteilheit2mA/V
Amplification Factor (μ)Verstärkungsfaktor
Output
Output PowerWechselstromleistung2.5W
Heater
Heater VoltageFadenspannung7.5V
Heater CurrentHeizstrom1.1A
Notes
Filament voltage stated as 7.5 V in the RV218 Telefunken datasheet; the RV258 datasheet (same book, adjacent page) states 7.0 V for the identical tube. Reference indexes list 7.2 V. The discrepancy likely reflects rounding — both tubes operate from the same nominal ~7 V filament supply.
Maximum ratings are Va=440V and Pa=24W. The datasheet explicitly states that for higher loadings (Va >440V or Pa >24W), the RV218 must be replaced by the RV258.
Extensively used in transmitter service. When paralleling multiple tubes, the datasheet warns of a risk of self-oscillation at ultra-short (UHF) wavelengths.
A special grid construction prevents 'Durchstoßen' (grid emission / secondary emission breakthrough), a known failure mode in early DHT power triodes.
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): nsyit.
Pin Layout — B4
1Filament (+)
2Anode
3Control Grid
4Filament (−)
Socket-Compatible Tubes ⚠ Not electrically compatible