Fender Deville with slight oscillation/flange sound

[Andrew58]

Well i have a really difficult problem its allready been to one repair shop and even after getting on the phone with fender they counldnt figure out what was happining.
Ok the probelm is kinda slight but basically when you strum the guitar nice and strong after you release and let the sound slowly fade you start to hear this weird phaseing flangeing kinda oscilation after it starts to get pretty quiet its hard to notice right away but you can cear it in the audience and it shouldnt be doing this. If any one has even the slightest idea of whats causeing this and what to do i would be so extreamly thankfull for this.

[mikeboone]

Just a couple of thoughts...

-Have you checked/replaced any tubes? See other posts about "swirl" with regards to tubes and matching. If, for whatever reason, one of your power tubes current draw or transconductance has changed significantly.....

-You should also check your bias current if it hasnt been done. From tinkering, I have found low bias current can make an amp sound funky.

-How old? It may need to be re-capped if it has some years behind it.

[Andrew58]

Yeah i changed out the original jj tubes with groove tubes and the same problem occured. Also i checked the esr of the caps with my meter and the all seamed to be in spec accept for the 22uf500 volt caps the messured 2.4 ohms which was alittle high but my esr is running at around 60khz so i have to take into effect capasitive reactance when i A/B it to some good 22 450 volt caps they only measured about 1.5 but maybe the were alittle better qaulity so that could be it. Im thinking of trying all the caps with my high voltage cap tester as well. I believe the bias is correct but ill double check. So maybe its a common swirl kinda distortion/oscillation? ill search on that as well thanks

[Andrew58]

well everything seams to check out so far any other ideas from anyone?

[Enzo]

Isolate the problem.

(Hot Rod DeVille or Blues DeVille?)

COnnect the amp to a different speaker cab. Still sound that way through them?

And plug the DeVille speakers into the output of some other amp and play it through them. They sound OK?

A rubbing voice coil can sound that way. And that was my first reaction to your description - rubbing voice coil.

And I am hoping the speakers are not plugged into the extension jack instead of the main jack.

If your filter caps were leaky or weak, you would get hum, not weird stuff.

Otherwise, does the reverb being on or off matter?

How about plugging the guitar into the FX return. SOund OK there or still funky? And send the FX send to some other amp for a listen to it. Same question.

ALl these things will narrow it down to a segment of the system.