Microphonic Tubes?

[Nubbs]

Hi all,

I have a 5:25 with the 10" speaker and last night I tried something that I saw on this site.

Instead of running both the master and the gain at around 9 to 11 o'clock and 12 to 2 o'clock for the master, at the 25 watt setting, I set the gains to 4 to 5 o'clock and the master at 9 o'clock. EQ's at 10 to 12 o'clock for both channels.

The sound was good and a bit compressed, but still very enjoyable. BTW, the guitar is a Taylor Classic Solidbody with the smaller humbuckers.
What caught my attention was at about 8th to the 10th frets in single note leads, on either channel, I was hearing a high pitched sound off the tail of the notes.

It only could be heard right after hitting the note and it was only a fraction of a second. It did not continue and it seemed only to be heard high up the fret board.
Is this caused by one or two of the tubes going microphonic?

Nubbs.

 

[GD_NC]

That sounds like it may be a power tube going bad. EL-84s sometimes start to produce weird harmonics when they get old.

Those tubes run hot and don't last all that long. If you haven't changed them in the last 12-18 months it's probably a good idea anyway.

 

[Bob Womack]

Another possibility is a hardware rattle. I had a similar sound once and was ready to chalk up the speaker then realized it was a loose speaker mounting screw allowing the washer to rattle. Another time I had a similar sound in a Marshall and it turned out that I had left the tube cage slightly loose when I was last in. When the amp is loud, ANYTHING not tied down can sympathetically hum, buzz, or rattle. One thing to do is turn the amp around and remove the back. Then play the note, cause the rattle or buzz, and run your hand around the various pieces of hardware trying to dampen the buzz while avoiding hot and electrically connected items that could burn or bite you. Because new speakers and tubes cost money, I always tend to try everything else first. I found the two cases above by this method.

Bob