Tube-number record
U18/20
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BrandMarconi
ClassRectifier
Base4-pin
Construction
Primary TypeDiode
Rectifier TypeFull-Wave
EnvelopeDome top tubular
Sections2
Filament / Heater
MaterialDirectly heated
Absolute Maximum Ratings
Plate Voltage850 V
Cathode Current275 mA
Audio Performance
Key Features
- Directly heated
- Bi-phase half wave
- Capacitor or Choke input
Typical Operation
| Mode | Plate V | Gm (µmhos) | Rp (Ω) | µ | Plate mA |
|---|---|---|---|---|---|
| Capacitor Input (Case 1) | 500 V | — | — | — | 250 mA |
| Capacitor Input (Case 2) | 850 V | — | — | — | 125 mA |
| Choke Input (Case 1) | 550 V | — | — | — | 275 mA |
| Choke Input (Case 2) | 850 V | — | — | — | 150 mA |
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