Tubes Became Microphonic

Nothing wrong with your pre-amp. Just a microphonic tube. Not unusual, especially with NOS. From what I understand its not all that unusual with NOS - you want to have them screened for noise before you buy them. FWIW I've used some new production EH's. They ain't that bad! Give them a try.

Thanks, Mark at Rogue thinks the same. I'm putting back in the stock EH's and sending the NOS back for testing. The NOS was screened, a matched quad purchased from Rogue. You gotta love their customer service. Mark actually answered the phone when I called first thing today. I might try the new EH's, cheap enough.

Also remember that NOS tubes will last considerably longer than the current crop of Chinese and Russian tubes. And they WILL sound much better!

And PLEASE don't use that tired old cliche that manufacturers "voice" their products for current production tubes!

It can happen to any tube. If the tube makes it past 250 hours it'll probably last it's expected life.

You might want to look at tube dampers. I recommend them but with reservations. They can create a more quiet background although I couldn't say they improve the sound. If they do it's not very much.

On the negative, I think they may give tubes damper memory meaning your tube is more likely to get noisy or microphonic if after having damped it for a month you remove the damper. This can seriously impair your tube rolling.

The reason for using them is that they may increase your tube longevity and may also prevent your tube from becoming noisy or microphonic oin the first place. I've also successfully used dampers to quell microphonic tubes that I would have otherwise discarded.

I'd use them on expensive tubes if I liked the sound and I was pretty sure I was going to keep them, but no tube rolling after that.