What does the “LPS” or “WXT” on my tube mean – can you also buy it without the suffix?

Both “LPS” on the 12AX7LPS and “WXT” on 6L6 and 5881 types are so-called suffix designations, just like with 5U4GY, 6L6WGC or 6SN7GTB. In addition to the standard properties, these suffixes describe further details. Examples:

LPS = long plate spiral heater; robust, bifilar heater for low hum

WXT = ruggedized; robust version, higher voltage rating with the 5881WXT

WGC = ruggedized, glass version C, stable and update version C

GTB = glass container, straight construction, update version B

GA = G, coke bottle version, first update A

Y = metal version

S = with JJ spiral heater, bifilar heater = low hum

In most cases, especially with current tube audio devices, the suffix only plays a minor role. Taking the datasheets and operating manuals into account, the tubes can usually be exchanged. If in doubt, please ask.