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Help Diagnose Tube Preamp Problem

I have a George Wright preamp along with his mono 3.5 amps. I recently started hearing some noise or crackling through my speakers at various times. When I turned the system on the other day, it was very loud for a couple of seconds, but then went away. I've done some research and "tested" the tubes by gently tapping them with a pencil, and the weird thing is the tubes in the preamp all give off a ping that is not solid like the tubes in the amps (I don't believe the tubes in the preamp all went bad at one time). Even stranger, if I tap on the metal on/off switch, this also pings through the speaker as if it is somehow getting picked up by the current. Something strange going on, anyone with any ideas of the problem? thanks
skf3636
marakanetz's avatar
marakanetz
5,473 posts
 
Did you check bias?
Tubes that are out of bias deeply might not be good anymore and certaly can pick up microphonies.

If the amp is new and tubes are deeply out of bias or you shouldn't bias these amps at all(have manuals?), you should contact the manufacturer or dealer.

At this point I would assume that one or more tubes per each channel went bad and would not continue to use them.
You should perform bias procedures with dummy resistor connected instead of speakers until you get them all biased properly.
ahendler
416 posts
 
I don't think the preamp which he is talking about has adjustable tube biasing. A lot of preamps will ping if you tap on the tubes and does not mean that they are bad. Does the pinging get worse as you turn up the volumn?
ahendler
416 posts
 
Another question. Does your preamp have the switch on the back for low and high gain? If on high switch to low gain and see if this helps solve your problem.
marakanetz's avatar
marakanetz
5,473 posts
 
I don't think it's preamp. I think it's amplifiers. Tapping tubes isn't a good idea at all.
opus88
529 posts
 
I agree with Marakanetz on both points, especially the loud crackling, which typically indicates a problem with amp output tubes.
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