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    ST-70 without a load

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    ixe13

    Posts : 18
    Join date : 2012-07-11

    ST-70 without a load

    Post by ixe13 on Wed Dec 05, 2012 7:29 pm

    Hi,

    Once in a while on ebay you can see a vintage ST-70 on sale, with a bunch of photos.

    More than a few times, though, I've noticed the seller show the amp turned on to show that it's working fine, which is very nice, very upfront to do that, I think,
    Buuuut, the amp in on without speakers connected to it Shocked

    Nothing conneted to the input, nothing connected to the speakers output...

    Obviously, the seller doesn't know much about tube amps I suppose. Isn't it risky to do something like that?

    If the amp is on idle, what are the chance that it could cause some problems?

    Thanx for any thoughts

    Yves

    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST-70 without a load

    Post by Bob Latino on Wed Dec 05, 2012 8:06 pm

    Hi,

    Personally, I won't turn an ST-70 amp on or any tube amp without a load (the speakers connected). Now in reality, the amp will probably be fine as long as the amp is "on idle" with no music playing. As an aside, I have seen ST-70's that would not bias properly without the speakers connected. One that I recall years ago gave a "cycling bias" with no speaker connected. The bias kept going up and down, up and down above and below the set bias point. When I connected the speakers on this particular amp, the bias settled right down and held steady.

    Bob

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