841

Power Triode — DHT — UX4

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RCA

↗ TDSL ↗ Radiomuseum

Known Equivalents & Substitutes

VT-51

Similar Tubes (Not Drop-In Compatible)

801A

Same UX4 base and similar filament voltage (7.5V vs 6.5V), higher Pa_max (20W vs 15W); not a drop-in replacement due to different filament requirements

843

Same Pa_max (15W) and Va_max (450V) transmitting triode but different filament (2.5V/2.5A) and UY5 base; not pin-compatible

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Plate Voltage (max)450V

Anode Dissipation (max)Plate Dissipation (max)15W

Cathode Current (max)Plate Current (max)60mA

Typical Operating

Anode Voltage (typical)Plate Voltage (typical, Class A)425V

Grid 1 Bias VoltageGrid Voltage (Class A)-40V

Anode CurrentPlate Current (Class A)18mA

Anode ResistancePlate Resistance9,600Ω

TransconductanceTransconductance

Capacitances

Grid-to-Plate CapacitanceGrid-to-Plate Capacitance3.7pF

Grid-to-Cathode CapacitanceGrid-to-Filament Capacitance2.6pF

Anode-to-Cathode CapacitancePlate-to-Filament Capacitance1.4pF

Heater

Heater VoltageFilament Voltage6.5V

Heater CurrentFilament Current1.25A

Notes

DHT tube: the thoriated tungsten filament serves as the cathode; there is no heater-cathode isolation.
Maximum plate current is 60 mA.
Designed primarily for RF oscillator and Class A amplifier service at plate voltages up to 450V.
Class A amplifier at Va=425V: Vg=-40V, Ia=18mA, mu=25, gm=2.6 mA/V, ra=9600 Ohm.
Filament may be operated on AC or DC. When AC-operated, grid bias voltage is referenced to filament midpoint.

Pin Layout — UX4

1Filament +

2Plate

3Grid

4Filament -

Socket-Compatible Tubes ⚠ Not electrically compatible

12A 26 2A3 30 300B 31 40 45 50 71A 801A 842 845 UX112A UX199

References

https://frank.pocnet.net/sheets/049/8/841.pdf
https://tdsl.duncanamps.com/show.php?des=841
https://www.radiomuseum.org/tubes/tube_841.html

2.6mA/V

Amplification Factor (μ)Amplification Factor25—

VT-25

VT-52