Uknown numbers marked on tubes (pix inside). What are they?

Does anyone know what they mean? Could they have any significance in terms of where they should be placed in my Mark IV?

I'd assume they're some kind of ratings or test numbers. But even if I'm right, I wouldn't know what that means in terms of how to match them up, bias them, and so on.

Characteristic measures. Not sure of the scale used but all mine installed in my amp now are marked/tested around 24 / 2.4 for Boogie bias.

You want to try to keep pairs within 10% or less to keep them balanced in push-pull pairs. For power valves those are the inner and outer pairs. I've only ever had valve problems with out of range pairs/valves.

Less of an issue with preamp valves - go with what sounds good gain wise to you.

Let's assume they mean gain on the 12ax7. Should the ones with higher gain go early in the chain?

Gain isn't measured that way and ECC83's are pretty uniform in their gain levels.
83's @100 mu (μ)
82's @ 17 mu (μ)
81's @ 60 mu (μ)

Those markings just look like pairing codes to me. Their meaning reliant on the person and tool used to measure them.
On the preamp valves people had a fascination with balanced phase inverters a few years back. Perhaps the numeric markings on the preamp valves are something to do with that nonsense.

godisme said:

Does anyone know what they mean? Could they have any significance in terms of where they should be placed in my Mark IV?

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Those numbers is from somebody that has tested his tubes on a tube tester. On the preamp tubes it is written the gain on both channels. The preamp tubes channels don't need to be match for guitsr amps. The power tubes is also tested it seems, the number don't mean a lot, but it is important the power tubes are matching.
PS, every tube tester brand got a different scale and methods measuring tubes, so take those measurements with a grain of salt

Ok but if this is gain, should the strongest ones go first in the chain? Does it matter where they should go in depending on which half is stronger?

For example, let's assume V3 (left side of the tube) is contributing to the amount of gain on Lead channel, so should I put in the tube which has the highest rating on the left side? Do you know what I mean?

Those numbers dont represent gain,gain is measured as "mu" or amplification factor.A 12AX7 should have a mu or amplification factor of around 100.So if those numbers representd mu,those tubes would be dead.Those numbers most likely are plate current measurements,depending on the plate voltage the tester has those numbers will vary,could be .5 at 100 volts on the plates to 1.5 or so at 250v's.Pay no mind to them on the preamp tubes.You just have to roll them around in the amp to find what sounds best in what position.