The Electro Harmonix tubes are basically Sovtek.
The EH is the tube supplied in the Wolcott amps, and I have tried several tubes against the EH since buying the Wolcotts a couple of years ago. First, there is very little difference between the Sovtek and EH, the differences sited by Avguygeorge when compared to Svetlana is pretty much dead on. The other tubes to try are the Tesla E34 L, which is the best of this bunch, unless you can afford Mullards. Mullards are so much better than all of these that the discussion is ended when they are plugged in for the first audition.
Of course money is always a factor. The Tesla, EH and Sovtek are all similarly priced, the Mullards are expensive, even used.
The EH is the tube supplied in the Wolcott amps, and I have tried several tubes against the EH since buying the Wolcotts a couple of years ago. First, there is very little difference between the Sovtek and EH, the differences sited by Avguygeorge when compared to Svetlana is pretty much dead on. The other tubes to try are the Tesla E34 L, which is the best of this bunch, unless you can afford Mullards. Mullards are so much better than all of these that the discussion is ended when they are plugged in for the first audition.
Of course money is always a factor. The Tesla, EH and Sovtek are all similarly priced, the Mullards are expensive, even used.