Are you using the JJ Blue tube or the clear. I have found that the JJ Blue is a mellower tube with better bass extension. I have also heard that the Svetlana C is a reproduction/copy of the Mullard. I would stay away from NOS power tubes not only because of price but differential wear which will mean some tubes will only put out very marginal power and die quickly. On top of that the price has given rise to countless counterfeits.
