st70

st70

Postby handyboy » Sat Nov 13, 2004 8:38 am

am currently trying out an st70. It seems to produce a humming sound on my left speaker. I presume its a ground. What can i do?
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Postby mozilla » Sat Nov 13, 2004 11:46 am

Gamby,

Did you try swapping tubes left to right? Try swapping the 7199's first then the el34's. If the hum moves w/ the tube, it's probably a bad tube.

Do this also w/ the tubes of you preamp. Unless you are using a passive.
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Postby amandarae » Sat Nov 13, 2004 4:41 pm

In addition to the excellent suggestion above, if all you tried does not eliminate nor moved the sound, then it has to be the quad filter caps which un-modded Dynaco ST-70 is notorious for. A weak section of the caps will almost certain to introduced hum to a certain channel where it is being use.

In the event that the filter cap was already replaced or modded, but the proper star grounding was not cautiously observed, hum of the nature you described will emerge periodically or sometimes permanently.

Also, make sure that the rectifier (5AR4) tube is not faulty. But of course, try to isolate if it is really the amp giving the problem and not other component.

Goodluck!
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Postby handyboy » Sat Nov 13, 2004 7:25 pm

Thanks for the help! will do that!
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