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Using 12au7 vs, 12ax7?

Posted by heyeugenio (A) on November 17, 2007 at 17:14:25

Hi fellow inmates,

I've been rolling all afternoon. I picked up a TAD-60 (previously owned an upgraded TAD-60) from a friend today.

The amp uses 2 12au7's and a single 12ax7. Using some of my old stock 12ax7s caused the amp to hum audibly via speakers so I threw in a Mullard CV4003 and, voila, no more hum.

I was sitting here enjoying tunes when it dawned on me that the cv4003 is a 12au7 variant not a 12ax7.

From my recollection, one has greater gain than the other but from what I'm hearing here, the difference is negligible at best.

So, long story short, is it ok to continue to use the nice and quiet cv4003/12au7 variant in place of the 12ax7?

The reason I no longer owned the previously upgraded TAD was because the hum drove me nuts and I obviously didn't discover that some input tubes don't exist well with others in certain amps. I've since moved my gear to another room and I wanted to take the chance on another TAD.

Any insight on this would be greatly appreciated!

TIA and happy listening!

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