Thank you Arfa. I did change the tube, but I will try another one. I
don't have a scope or signal generator, so hopefully it is the tube. I
was considering replacing all the filter caps but if it is not the tube
I might be better off taking it to someone. Thanks again.

Arfa Daily wrote:

wrote in message
oups.com...
When I hit a certain a certain frequency, it is followed by a distorted
sound. Also certain notes have a vibrato like sound. I have eliminated
all possibilities but the amp. I am wondering if it may be the filter
caps or if anyone has any ideas. Thanks.


I think I am correct in that this amp has a tube (valve) front end ?? If so,
the tubes themselves would be my next suspicion, as such resonances can
occur as a result of loose electrode structures. Is the problem affected by
how loud the unit is turned up ? If so, could be a power supply problem.
This amp has pretty meaty output stages, and poor power supply regulation
could lead to problems with the front end. I think that the next place I
might be going after that, is to try to set up the problem with a signal
generator. It should then be fairly easy to track it down with a 'scope.

Arfa