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Post by brayks on Mar 20, 2009 5:09:25 GMT -7
I was looking to get a little more clean head room out of my Maz JR and noticed on the forum that a lot of people recommended swapping the PI out for a 5751.
Being in a hurry and trying to conserve cash, I purchased a JTL-5751 Tungsol NOS "o" with mismatched sections.
After swapping it in I did notice some more clean head room but something was off. I don't know how to describe it but the amp just didn't have the same vibe or was not as alive.
Looking further into the tube mismatch it appears one side is quite higher than the other (2.7ma/3.7ma).
After thinking about it a bit and the function of the PI, I thought, wait a minute, the mismatch probably does matter.
My questions is how important is a close match for the PI, what would one expect the sonic result of a mismatched PI tube to be, and what should I expect if I bit the bullet and do what I probably done in the first place; buy a NOS 57571 with matched sections?
Any recommendations on 5751's for the PI of my Maz JR?
I would greatly appreciate some response and help on this......Thanks.
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Post by benttop (Steve) on Mar 20, 2009 5:39:51 GMT -7
You really want both sections to be matched for that chore. Each side drives one of the EL-84's in the power amp. If they aren't matched it will sound "off" for sure.
All is not lost however because probably the most popular location for a 5751 in the Maz Jr is in V1. And you do not care if it's matched in that location. Try it.
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Post by brayks on Mar 20, 2009 6:44:55 GMT -7
Thanks Bentop, I was gonna try it just for kicks. I would assume I would loose overall volume as it has less gain than the 12ax7. Any other expectations?
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Post by John on Mar 20, 2009 7:19:11 GMT -7
I use a 5751 in my Maz Jr....but I put it in V1. I want the full 12ax7 in the PI to push the power tubes, but I like a cleaner preamp.
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Post by benttop (Steve) on Mar 20, 2009 8:29:22 GMT -7
Thanks Bentop, I was gonna try it just for kicks. I would assume I would loose overall volume as it has less gain than the 12ax7. Any other expectations? None from me, as I don't do this. John is the resident expert on using the 5751 if you ask me. He's been doing it for a long time and likes it just fine.
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