The problem with responding to this is that Mullard EL34, like other tubes, respond differently in different circuits. It depends on if they are run in triode, ultra linear, etc. Also, you need to consider how long a life you will be getting from these old rare tubes in your particular amp. I have owned amps that literally trashed EL34 tubes in as little as three months! Other amps run for several years with no appreciable damage to the vital trans conductance of the tubes. Obviously, if your particular amp is hard on tubes, this would be a horrible expense to keep it fed with such rare and hard to find tubes. In direct response to your question, I think the Mullard tube does offer a certain magic in the midrange and mid bass, but they are sometime lacking in deep bass and sparkle in the extreme top end. Other tubes to try are Seimens EL34 or AEG Telefunken (which are built by Seimens), also some good new tubes to try are the Tesla EL34 and perhaps there are even some substitute tubes that can be used in place of the EL34. You will need to first check with your amp manufacturer. Some possible substitute tubes are 6L6, 5932, KT66 or KT77. This depends GREATLY on how the amp is designed and how it is run (Triode, etc.) and what bias it uses, and how the circuit is designed. It is worth investigating, particularly considering what you are considering spending.
