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    ST-70 without a load



    Posts : 18
    Join date : 2012-07-11

    ST-70 without a load

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


    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


    Bob Latino

    Posts : 2382
    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


    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.


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