New Tube Report: Day 2

Turn it up, Dude!

After a few more hours of tube burning, I put the Delta with the JJ's through the paces again. Everything was about the same.. possibly a bit better.. until I turned it up. At which point it got MUCH better!

Push a little juice through this thing now--post-gain anywhere past 10 o'clock--and you've got yourself some beautiful, crisp tone. If you push the mids up, you get a nice "box" Vox sound. The frequencies are so much more well-defined than they were. I am very pleased.

I also played with my possibly-microphonic pre-amp section for a while. If you turn the amp all the way up, even with no guitar connected, it quickly starts to make a feedback-like "singing" noise.

With the tubes well-heated, I gently tapped eached tube with my fingernail. The pre-amp tube in position 1 (the farthest from the power tubes) sounds almost like a bell when you do this, and immediately starts in with the "singing". Once this has been done, you can also make the tube in position 2 "tong!" slightly. And you can also bring back the singing by tapping the leftmost two power tubes. With the amp turned almost all the way up, you can get this same noise (after you've badgered it for a while) just by putting your hands close to the tubes! Like feedback on a microphone.

I experimented first with swapping the position 1 & 2 pre-amp tubes. This seems to calm the "problem" tube down quite a bit. But doesn't make the issue go away. In fact, it seems to make the power tubes more succeptible to ringing. : [

Secondly, I tried swapping out JJ pre-amp tubes, one at a time, with the Chinese 12ax7s that I am replacing. They may not be much on tone, but those CN tubes are dead quiet. Still, when you put the problem JJ in line w/ the Chinese tubes, the JJ still rings.

Today I am burning the JJ's in for several more hours, but I'm not expecting a change. The good news is, I love the way the tubes sound, and I can't wait (I keep saying that, don't I?) to get the new speakers in it, and try the whole deal with the 1500. The bad news is, I think, that I'm going to need a replacement for this one tube. Guess it's time to email Bob at Eurotubes and see what he has to say!

Anybody have experience with microphonic tubes? Bill..? Kirk..? Am I right in my thinking here?