Tube cross-reference
U404 alternatives, equivalents, and replacements
Review exact electrical variations and directional substitutions recorded for the U404 rectifier - half wave. Compare core specifications and verify every restriction before using a replacement.
Where U404 can be used as the replacement
In these recorded relationships, U404 is the replacement tube. The listed original tubes are not automatically suitable as replacements for U404.
Rectifier - Half Wave
The database records U404 as a possible replacement for31A3.
No special restrictions are recorded for this substitution.
| Specification | U404 replacement | Original tube |
|---|---|---|
| Tube type | Rectifier - Half Wave | Rectifier - Half Wave |
| Construction | Rectifier | Rectifier |
| Base | Not recorded | 8HB |
| Socket | Not recorded | Not recorded |
| Base pins | Not recorded | Not recorded |
| Sections | 1 | 1 |
| Heater voltage | 40 V | 31 V |
| Heater current | 0.1 A | 0.1 A |
Verify before substituting
Matching a base or heater voltage is not enough to prove that two tubes are interchangeable. Check pin connections, heater current, maximum ratings, bias requirements, warm-up behavior, and the equipment manufacturer’s service documentation before making a substitution.
View the complete U404 specifications →