Tube cross-reference
21FP4 alternatives, equivalents, and replacements
Review exact electrical variations and directional substitutions recorded for the 21FP4 specialized - cathode ray. Compare core specifications and verify every restriction before using a replacement.
Replacement tubes for 21FP4
The following tubes are recorded as possible replacements for 21FP4. This direction does not establish that 21FP4 can replace them.
Specialized - Cathode Ray
The database records 21FP4A as a possible replacement for21FP4.
No special restrictions are recorded for this substitution.
| Specification | Original tube | Replacement |
|---|---|---|
| Tube type | Specialized - Cathode Ray | Specialized - Cathode Ray |
| Construction | CathodeRay | CathodeRay |
| Base | Not recorded | Not recorded |
| Socket | B12A | B12D |
| Base pins | 12 | 12 |
| Sections | 1 | 1 |
| Heater voltage | 6.3 V | 6.3 V |
| Heater current | 0.6 A | 0.6 A |
Where 21FP4 can be used as the replacement
In these recorded relationships, 21FP4 is the replacement tube. The listed original tubes are not automatically suitable as replacements for 21FP4.
Specialized - Cathode Ray
The database records 21FP4 as a possible replacement for21FP4A.
No special restrictions are recorded for this substitution.
| Specification | 21FP4 replacement | Original tube |
|---|---|---|
| Tube type | Specialized - Cathode Ray | Specialized - Cathode Ray |
| Construction | CathodeRay | CathodeRay |
| Base | Not recorded | Not recorded |
| Socket | B12A | B12D |
| Base pins | 12 | 12 |
| Sections | 1 | 1 |
| Heater voltage | 6.3 V | 6.3 V |
| Heater current | 0.6 A | 0.6 A |
Specialized - Cathode Ray
The database records 21FP4 as a possible replacement for21FP4C.
No special restrictions are recorded for this substitution.
| Specification | 21FP4 replacement | Original tube |
|---|---|---|
| Tube type | Specialized - Cathode Ray | Specialized - Cathode Ray |
| Construction | CathodeRay | CathodeRay |
| Base | Not recorded | 12L |
| Socket | B12A | DUODECAL6 |
| Base pins | 12 | 12 |
| Sections | 1 | 1 |
| Heater voltage | 6.3 V | 6.3 V |
| Heater current | 0.6 A | 0.6 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 21FP4 specifications →