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Old 26th October 2008, 11:25 PM   #1
mt1962 is offline mt1962  Canada
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Default New matched tubes - where to use them

I have finished an ST70 build and found one of the EL34B's dead.
I have ordered a new matched pair ?

Do I put the new matched pair both on one channel/side or do I split them and mix with the other two matched pair for the best results ?

Do I need to rebias after putting in replacement (same type) tubes ?

I am sure this may be a trivial question but I would appreciate your thoughts.

As a fianl question, do I run any chance of damaging the amp if I run with three operative EL34B's while waiting for the replacements ?
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Old 26th October 2008, 11:29 PM   #2
SY is offline SY  United States
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Use the matched pair in one channel- their matching controls the ripple rejection and distortion. The "odd" tube from the pair can be kept as an emergency spare, but unless you can find another tube matched to it, it will be less than optimal.

Yes, you will need to rebias. Check it often for the first 10-20 hours of tube use.

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Old 27th October 2008, 12:08 AM   #3
anatech is offline anatech  Canada
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Hi mt1962,
I'll just add to this. Order a matched quad. It doesn't cost any more than two matched pairs and you can just stick them in. Then after wearing, you may find the pairs match better another way.

Do not run only one tube in a push pull amp.

-Chris
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