[Amps] Filaments show different brightness

[Pete Smith]

Today I was running my SB-220 with the case off, and noticed, to my surprise, that the filaments of the two tubes show quite different brightness reflected off the desk under the amplifier, even on standby.  Key-down, the brighter of the two tubes also appears to be taking the lion's share of current, judging by the extent to which the plate of that tube brightens up when key down, compared with the other one.

Is this to be expected, with pairs of tubes where I have made no effort to match them.  I've been running this pair of tubes through several years and a number of fairly intense CW contests.  Grid and plate current totals are well within the expected values.  I have a couple of spares - should I make an effort to match them more closely?

73, Pete N4ZR
The World HF Contest Station Database
Full details on 3165 contest stations
at http://www.pvrc.org/WCSD/WCSDsearch.htm