Tube cross-reference
421A alternatives, equivalents, and replacements
Review exact electrical variations and directional substitutions recorded for the 421A power - triode. Compare core specifications and verify every restriction before using a replacement.
Replacement tubes for 421A
The following tubes are recorded as possible replacements for 421A. This direction does not establish that 421A can replace them.
5998
Communications And Special Purpose TubesPower - Triode
The database records 5998 as a possible replacement for421A.
No special restrictions are recorded for this substitution.
| Specification | Original tube | Replacement |
|---|---|---|
| Tube type | Power - Triode | Power - Triode |
| Construction | Triode-Triode | Triode-Triode |
| Base | B8-11 | B8-11 |
| Socket | UX4 | IO |
| Base pins | 8 | 8 |
| Sections | 2 | 2 |
| Heater voltage | 6.3 V | 6.3 V |
| Heater current | 2.4 A | 2.4 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 421A specifications →