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    [ST-70] EL-34

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    Nicola

    Posts : 12
    Join date : 2011-11-20
    Location : Roma (Italy)

    [ST-70] EL-34

    Post by Nicola on Wed Feb 15, 2012 5:20 pm

    Hi everyone!
    My fully original Stereo 70 has a bad EL34 tube. It still has these four '60 Philips Miniwatt:



    I've only a couple of questions:

    1) I would like to replace the bad tube only. Is it a big heresy, to use the amplifier with 3 vintage tubes and one new and from a different brand?

    2) I can easily find EL34s from JJ-Electronics and Electro-Harmonix. Which one do you think is the better one, in my situation?

    Thank you in advance Very Happy

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: [ST-70] EL-34

    Post by Luddite on Wed Feb 15, 2012 5:55 pm

    Nicola wrote:Hi everyone!
    My fully original Stereo 70 has a bad EL34 tube. It still has these four '60 Philips Miniwatt:


    I've only a couple of questions:

    1) I would like to replace the bad tube only. Is it a big heresy, to use the amplifier with 3 vintage tubes and one new and from a different brand?

    2) I can easily find EL34s from JJ-Electronics and Electro-Harmonix. Which one do you think is the better one, in my situation?

    Thank you in advance Very Happy

    With the original circuitry, you need to have both tubes on one channel closely matched. At the very least, I would replace with a matched pair, but it would be better to replace all four with a matched quad of the same brand tubes.

    Best Regards,
    Charlie

    Blitzen

    Posts : 47
    Join date : 2009-07-10

    Re: [ST-70] EL-34

    Post by Blitzen on Wed Feb 15, 2012 11:24 pm

    On the plus side, the three remaining tubes still have value if they're in good condition. I'm pretty sure those are actually Mullard tubes, which have a pretty high standing among the guitar amp crowd. If two of them still match up, they can be sold for probably close to what a new set of 4 costs...!

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: [ST-70] EL-34

    Post by PeterCapo on Thu Feb 16, 2012 12:42 am

    Are you sure one of the tubes has gone bad? Did you put it on a tube tester?

    Given that different brands of tubes have different sonic signatures (perhaps even through different production runs of the same tube), I would be concerned that one different brand of tube out of four would result in one channel "sounding" different from the other channel even if the tubes are matched and the bias is set correctly. Channel-to-channel consistency is very important, IMHO.

    I would suggest replacing all four. Or, perhaps just replace two, using one new one and one of the originals in each channel. Of course, each channel's pair should be matched. Try contacting tctubes.com. He might be willing to have you send-in your tubes and he might try finding a match for two of them, although this might not be possible if the other good originals are weak. In the future you might also consider the bias kit from Dynakitparts.com where you can bias each tube individually (though I would still keep brand or brand-mixing consistent from channel-to-channel.)

    Nicola

    Posts : 12
    Join date : 2011-11-20
    Location : Roma (Italy)

    Re: [ST-70] EL-34

    Post by Nicola on Thu Feb 16, 2012 6:34 am

    Thanks everyone!

    PeterCapo wrote:Are you sure one of the tubes has gone bad? Did you put it on a tube tester?
    I have a problem, described months ago in this topic: http://dynacotubeaudio.forumotion.com/t1018-st-70-noise-when-heating-up
    Conclusion was that there is one bad tube.
    Unfortunately I can't test tubes; actually I'm even not sure to have on each channel the same original matched pairs of tubes, because I moved them to figure out which one was bad. Last, I'm in Italy and I wouldn't like to ship my tubes far away, and waiting a lot of time.

    Even if I would like to take my ST-70 as original as possible, I think I'll get four new matched tubes so I'll be sure they'll be properly matched.

    Any suggestions about the tube brand? I've found Electro-Harmonix, JJ and even Bugera (I've never heard about it).

    Another time, thank you for your quick and expert suggestions!

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: [ST-70] EL-34

    Post by PeterCapo on Thu Feb 16, 2012 1:07 pm

    In my experience, the Electro-Harmonix has more top-end extension, more detail and more snap than JJ. I have an older set of JJ E34L that are more laid-back than the EH, but still good, depending on your taste. However, in my experience and based upon reports from others, JJ quality control and manufacturing consistency seems somewhat variable, so it may be hard to predict what they might sound like. Not familiar with Bugera.

    HiGHFLYiN9

    Posts : 3
    Join date : 2011-08-17
    Location : East Coast

    Re: [ST-70] EL-34

    Post by HiGHFLYiN9 on Thu Feb 16, 2012 4:48 pm

    I'm very happy with the SEC Winged C, they have a warm and lush sound with a buttery smooth midrange.

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