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New Build - distance between power tubes...

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  • New Build - distance between power tubes...

    Hi All,

    I'm working on a new build amp for myself. I picked a pretty small chassis/cabinet so it's a crowded build.

    What's the minimum distance between power tubes (6V6) that should be observed, when drilling and mounting tube socket holes?
    And what's the minimum distance between a power tube and a rectifier tube?

    So far, I've just been copying other amps I have or have seen. For example, I've noticed that some of the 80s Fender/Rivera amps have their power tubes a little closer to one another than the earlier classic Fender designs.

    This is all in the interest of 'measuring twice, and cutting once'.

    Thanks for the on-point responses,

    Bob M.

  • #2
    Hi Bob....

    Lots of posts on different threads regarding tube distance. Just do a search for "minimum distance power tubes."

    Here is one such thread - EL34world.


    • #3
      Thanks, Tom for your reply,

      Here's some more data - I've chosen to set the power tubes 1-7/8" apart from each other - that's center to center. The outside glass of each power tube would then be about 3/4" from one another. Now, that's the power tubes closer together than a classic tube design from Fender (think 60s~70s) but not as close to one another as some other tube amps I've seen in more recent times and in more recent designs.

      Further reading has seem to indicate that the only consideration in power tube proximity is the amount of heat the tube throws off - having very hot tubes too close to one another is not good. However, I'll be using 6V6 type tubes and these are not going to get too hot and I don't plan on driving the shit out of them either so I think heat dissipation will only be a moderate or even possibly small issue of consideration.

      I was also wondering about the proximity of power tubes to the speaker magnet and what possible effects that can have on tube performance, and sound/tone. As I said, this is going to be a very crowded build and it's a real 3-D puzzle to fit everything and give each component some space of its own without impinging on its neighbor. I tend to like speakers with big magnets and I tend to oversize the power handling capacity because of personal preference. So I'll have a big 12" speaker with a big magnet and two 6V6 power tubes hanging down (Fender style) in pretty close proximity to the speaker magnet (an inch or two away). I have one other amp I use all the time that sounds very good (mostly for rehearsals) that I re-built for my purposes. It's a (70s) Fender Vibro Champ (gutted) with the equivalent of a Fender Bandmaster (about 35~40 watts) built inside the VC chassis/cab (2x 6L6, LTP - PI, one channel, big 10" speaker, with, of course, a big magnet. It all fits together like a Rubik's Cube and the bottoms of the 6L6 power tubes are quite near the speaker's magnet however, I've noticed no bad effects from this. But inquiring minds want to know about power tube, speaker magnet interaction.

      I'm trying to think of all the ramifications of my design before I start cutting and installing, thinking it thru carefully so I don't end up with a pig in a poke.
      Thanks for any and all on-point responses. I've built quite a few amps with some pretty good successes but I'm still learning as well.

      Bob M.


      • #4
        Closest I ever saw was a Super Twin. Those struck me as a bit close for 6x6L6s, but it did good...

        I don't recall which, but one of the old tube "bibles" gave distances for different tubes ... I'll hafta check mine.

        "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
        "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
        "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -


        • #5

          See thread 18428. That thread is titled "tube/speaker magnet proximity." I found another thread on - Speaker magnet proximity to tubes. Perhaps these two threads might shed some light on the topic.


          • #6
            Have you installed the valve sockets yet? It may be worthwhile rotating the sockets so that the hottest direction of glass and radiation from the plate are at 90 deg to the next valve(s).


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