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tube match?

Can anyone tell me how close the readings on tubes need to be to run in the same pre? I have the following readings, I'm wondering if any are close enough to run in a 2 tube pre.

37/36 41/40 28/36 28/32 they are tung-sol 12au7's don't ask me which reading is for what, I don't have a clue. These are the numbers written on the tubes.
kt_88
kt_88 OP
242 posts
 
Here is the necessary info;

41/40 (JTL 12AU7 with "D" shaped getter ), 37/36, 28/32, & 28/35. All measurements recorded on EMC 205 tester, where 40 is spec for a new tube and 25 is "acceptable" as 65%.
albertporter's avatar
albertporter
4,949 posts
 
Looks like my suggestion to use the higher numbered and closest matched pairs was correct.

The D getter tung sol is probably a good tube. The other brand to try is Telefunken, they are my favorite among those I have tested.
fletchj
91 posts
 
Most often, tubes that match, within 10% is acceptable. If the numbers, came from the same tester, with the same settings, then you can use them, to match the tubes. The higher the numbers, the better, the tube tested.
kt_88 OP
242 posts
 
Cool, based on your imput, I would say I have 2 matched sets of tubes.

thanks
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