Valve matching with a KiT6550

[jdd308]

How important is valve matching with a KiT6550?

Over the years I am lucky to have collected a few sets of matched valves, and over the same years, one valve from each set except one has failed. Red glow, no output, sparks and I even dropped done and smashed it. Doh!

So each set has a value printed or written on it, the sets from Hotrox have two values. For example:
SED Winged C two at 77mv, two at 76mv. One valve with no output.
TungSol 6550 4 at 83mv, one glows red.
TungSol 6550 two at 76, two at 68mv. This set works fine.
TungSol 6550 4 at 58mv. TC 7.0. This set works fine.
TungSol 6550 4 at 68mv, TC 7.4, one smashed.
TungSol 6550 4 at 56mv, TC 6.7, one dead no output.

Can I use two matched pairs to safely make up a quad using the remaining working valves?

For example use two of the remaining TungSol 6550s 68mv in the left channel, and two of the remaining TungSol 6550s 56mv in the right channel?

Would there be a channel imbalance that I can hear? Anything else to be aware of?

Thanks as always,

John