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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
skf3636 OP
7 posts
 
Thanks for the responses. I'll try the quick method of cleaning the tubes/sockets. Both channels are affected. I'll also get the tubes checked at a local shop if I can't get it working properly.
jea48
4,415 posts
 
Both channels are affected.

Skf3636,

Both channels?...... Have a feeling it is something in the power supply. Could be a loose connection. Maybe a cold solder joint.
atmasphere's avatar
atmasphere
11,784 posts
 
Sometimes AC power switches can develop issues that will cause crackling. This is caused by bad contacts in the switch. Tapping on the switch can sometimes excite the behavior.

If you get a pinging sound by tapping on the switch, it is because vibration is transmitted from the switch to the tubes through the chassis.
skf3636 OP
7 posts
 
Update - I took Jea48's advice to clean the tube sockets and pins. After a little more research, I bought some deoxit gold at the local guitar center, sprayed it on every tube in the system, and unplugged and replugged every tube a few times. I then had to leave for a while, and when I returned I turned on the amps and there was absolutely no noise with the volume on or off. And the music sounded crystal clear. I think the cleaning worked, and for anyone landing on this thread in the future, I highly recommend using deoxit gold for periodic maintenance of a tube amp. Thanks again for all of the responses.
atmasphere's avatar
atmasphere
11,784 posts
 
Skf3636, the deoxit gold is good stuff, but should be used sparingly, particularly in tube gear! If I were you, I would pull all the tubes out, and carefully wipe down the sockets and bases of the tubes to remove excess chemical. Too many times, I have seen contact cleaners cause problems later on, as the chemistry can break down and become conductive in the presence of heat and high voltages. If that happens, you will first notice it as a loss of high frequencies.
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