Tube cross-reference
X81 alternatives, equivalents, and replacements
Review exact electrical variations and directional substitutions recorded for the X81 new (being researched). Compare core specifications and verify every restriction before using a replacement.
Exact variations of X81
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.
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 X81 specifications →