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Old 23rd September 2007, 12:00 AM   #1
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Default Tube Matching and Push-Pull

I have a push pull circuit that looks like this:

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I have a quad of tubes to use (12J5GT's). They all test good, but they are not quite matched. On my tube tester, one tests 100, two test 115, and the fourth tests 130 (never mind what those numbers might actually mean -- suffice it to say that >80 is "good"). Now, I know the answer is that I should come up with a matched quad, but, absent that possibility, is it better to pair the 115's on one side and the 100 and 130 on the other, or split the difference between sides?
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Old 23rd September 2007, 12:15 AM   #2
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I'd split the difference.

If you feel ambitious, you could stick a small resistor in the cathodes of the higher gm tubes to try to get them to match the lower gm ones.
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Old 23rd September 2007, 12:25 AM   #3
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Quote:
Originally posted by SY
I'd split the difference.
Sounds like a plan

Quote:
If you feel ambitious, you could stick a small resistor in the cathodes of the higher gm tubes to try to get them to match the lower gm ones.
The fact that these are $3 tubes suggests that I should just buy enough to make a matched set or two. But, thanks for the suggestion in case I ever use something more expensive, or dual, that needs matching.
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