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Thread: Power tube switching!

  1. #1

    Default Power tube switching!

    What about swapping out different power tubes in amplifiers designed for a specific type? Since the question keeps coming up, we thought it would be beneficial to have this as a sticky.

    Q: Will they physically fit?
    A: Yes, in most cases.

    Q: Does that mean the amp will operate correctly with the incorrect tube type installed?
    A: No, speaking strictly from an engineering standpoint.

    Q: Will flames and sparks ensue?
    A: No, assuming the tubes are good. EXCEPTION: Two/Ninety/Two power amp.

    Q: Is it safe to try it?
    A: Generally speaking, yes, if you know what you’re doing. EXCEPTION: Two/Ninety/Two power amp.

    Q: Will I like the sound?
    A: Maybe. You may believe that the different distortion character is the signature of the substitute, and that may work OK for you. In reality what you’re actually hearing is the sound of the substitute tube trying to function under a pretty significant handicap.

    Q: Who do I contact if I can’t get the bias set properly or don’t like the results?
    A: Contact the companies who promote this practice as a legitimate feature and ask them to explain why they promote something that every experienced design engineer on the planet will tell you is false.

    Q: Why are you guys so adamant that this is a bad idea when so many other amp companies promote tube switching as a design benefit?
    A: Because we feel we can deliver legitimate design benefits through superior design and engineering, as opposed to pitching a proven false concept that may sound good on paper but doesn’t really deliver.

    Q: Are you saying that other designers I respect are liars?
    A: No. Tube switching can be claimed to be a useful feature within a very broad (loose) interpretation of functionality:
    1) The operating parameters of the tubes in some designs may be such that no tube actually performs to its optimum potential. In that limited context, any type will “work”.
    2) They don’t really know. Many “designers” lack the engineering chops to know better or simply clone other company’s designs that make this claim.
    3) Herd mentality. This idea is now so universally engrained in the general discourse that they feel it is impossible to swim against that current – and justifiably so. If you don’t have the skill, knowledge or the stomach to fight it, you’re going to join in on the justification that “everyone else does it”.

    If you own a particular amp and wish you could hear it in a different dress so to speak, that’s perfectly understandable. If we were to tell you “yes, putting EL34s in a KT88 designed amp will get you 80% there”, we’d be lying. It’s more like 60% and the results would be so skewed that you wouldn’t know what changes are attributable to the tube character and which are due to flat out incompatibility.

    Someone might claim that their output transformer is designed to be compatible with several tube types. Unfortunately, transformer design criteria demands that such a transformer cannot be compatible with any one tube type. Since this is basically true for all tube amplifiers, there is no universally applicable response which justifies tube switching and at the same time explains away the complications.

    Last edited by sfryette; 10-09-2012 at 09:43 PM. Reason: To match with bolg updates...

  2. #2
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