david henman said:
...whenever i play a "G" note on my guitar, my amp makes a loud wheezing noise. a friend says its worn tubes or worn speaker. i suspect tubes - its been a couple of years, at least, since i re-tubed. i have spares. how do i check? replace each tube, one at a time? is there an easier way, without searching for a tube tester?
-dh
It's not 100% that it's tube or speaker, David. Most likely, but it could still be an internal problem.
If it's a tube it must be that the tube is vibrating inside and that a "G" is resonating to make the noise louder. I'd take a few layers of paper towel so I don't burn my fingers and press and hold each tube while someone plays a "G" note. If gripping the tube changes the noise (it may not totally stop it) then that tube is suspect. It can also be more than one, which makes things tricky.
Jeff is right in that a tube tester can't tell microphonics or tone/taste. Those have to do with our taste in what we hear and not if the tube is amplifying properly.
If you've got at least one extra 12AX7 you can "Easter EGG" the problem. Change out each old tube one at a time with the known good one.
If you can plug in a different speaker cab (don't worry about the speaker ohms for just a short test) that will tell you if the speaker is the problem. You can also have a problem with the glue and bracing of an old cabinet. Pushing on things while someone plays the guitar can often tell you if it's a corner letting go or whatever.
The other solution is just to never play any "G" notes... None
