Tube cross-reference
4125A alternatives, equivalents, and replacements
Review exact electrical variations and directional substitutions recorded for the 4125A power - tetrode (not beam) (over 1000v 100w). Compare core specifications and verify every restriction before using a replacement.
Exact variations of 4125A
These designations belong to the same electrical variation group. Their names may differ because of international standards, manufacturing tolerances, or materials, but they are recorded as electrically equivalent—not merely substitutes.
4D21 Power - Tetrode (NOT beam) (over 1000V 100W)
- Base
- Not recorded
- Socket
- J4
- Base pins
- Not recorded
- Sections
- 1
- Heater voltage
- 5 V
- Heater current
- 6.5 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 4125A specifications →