Factory description: Gold plated control grid for improved fidelity. Special plate alloy to improve plate dissipation. This is a hand aligned Beam power tube resulting in stable performance at higher power levels.
My observation: These are a wonderful addition to the JJ line and it's great to finally have a real new production KT66 that has all of the sonic qualities of the original! A very thick and rich sound with lots of harmonic complexity and a wonderfully smooth breakup when driven into saturation. These are killer in the Dr Z RT 66. We have been sending these to Mike at Z for a while now and he loves them! We are also using these in Mesa Dual and Triple Rec's all by themselves and in combination with KT88's and 6L6GC's. We have researched the proper grades to get the bias right where is should be with no bias mod. You can find kits in the online store!
Incase you have heard horror stories about the metal bases being connected to a pin and causing shorts, the culprits are the sovtek KT88 and KT66 tubes. You should all know by now that the fake russian tungsol KT66's are sovtek tubes and yes, the bases can cause shorts. This is NOT the case with the JJ Electronic KT66's and KT88's where the bases are isolated as they should be.
I mean, I thought you really F'n hated JJ's. 
