MY AMP loves everything except the note F. WHY?

[newguitarsmell]

My amp sounds absolutely gorgeous - then I hit the note F (particularly 8th fret A string) and I get distortion. Can somebody help me out? I tried a different speaker - no difference. I also tried a different tube --

Thoughts? Help? Should I just give up playing in the key of F?

[shooter]

I tried a different

I'd start at the other end, did you swap guitars

[newguitarsmell]

I will try that tomorrow....Why would my guitar be sending a crap F to the amp though?

[shooter]

I've been fixing broke things a LONG time, "why" is for the real engineers 

I don't play, can't tell E from A, one build the bass flabbed out, spent too much time trying to fix my amp, when I had a broke tensioner thingy in the bridge for the fattest string.

[newguitarsmell]

Tried two different guitars - still the scratchy sound but on different notes.

[shooter]

scratchy sound

that's a better description, but it leaves ALOT of possibilities
with the amp warmed up, say 5minutes, nothing plugged in, play with all the knobs, scratchy?

plug n unplug you're guitar 5-10times, then play, schratchy?

If no; with the chassis out, speaker plugged in, amp powered up, nothing at the input, take a wooden stick (chopstick) and wiggle n giggle wires, thump on solder connections, schratchy?

[plumcrazyfx]

Sympathetic vibration and microphonic preamp tube?

[galaxiex]

Is it a combo amp?

Some kind of resonant frequency thing.

I have a speaker cab that is "tuned' for the G at the 3rd fret 6th string.
Vibrates/rattles like hell on only that note. Any guitar.

If you sit on the cab and hit that note you get an "interesting" massage.... 

[Ed_Chambley]

Drop tune the guitar a whole step. 8 fret second should now be d sharp and fret 10 your f.


Does it stay at the 8th fret? Is so, lower your pickups. If not, check your filter caps.

[uki]

Had similar problem on one of my amps, did check all solder points, it fix the problem. Not saying it is the case but check it out.