Maybe, the Tesla E83CC tubes are. But, my experience with the 6DJ8/ECC88 is different. Pulling a lot from old HP scopes --- almost half will be noisy. I figured that those tube were designed to be impervious to mechanical vibrations and shocks, but not necessarily audio frequency feedback.
That's more of a result of the close grid spacing necessary to get the high transconductance of the 6DJ8/ECC88.
In fact, a tube of the same specs as a 6DJ8 really couldn't even reliably be built, using anything BUT frame-grid construction- standard plates and post-grids would never be able to have a low enough noise or microphonics level at those tight spacings, to even work new out of the box reliably. It's the frame-grid construction that makes it possible to have a tube with the parameters of a 6DJ8, in essence.
Regards,
Gordon.
