High pitched noise from my SOVTEK MIG100

[adamo]

I recently purchased a SOVTEK MIG100. It has 4 Groove Tube 6L6's in it that are about a year old. When the master and the volume are turned up it gets a high pitched kinda noise going, it's not feedback. I figured it was the speaker cable but it doesn't do it with my Musicman HD130 that only has a hum but it is from the 70's. This is from the late 80's or early 90's I believe. It also sounds like the sound could be louder it doesn't cut through the other instruments at band practice like it should. Any help would be appreciated. Thanks!

[52 Bill]

When the master and the volume are turned up it gets a high pitched kinda noise going, it's not feedback...It also sounds like the sound could be louder it doesn't cut through the other instruments at band practice like it should.

Well, if probably is feedback. It sounds like the amp is oscillating, internal feedback. This can be caused by any number of things, a bad cap, poor wire layout, a bad tube, etc.

This could also cause the power loss, as the amp is actually spending its energy amplifying the high pitch squeal, robbing power from the audio signal amplification.

[gomez63]

start by replacing the preamp (12ax7) tube(s) with known good ones, one at a time starting at the v1 position...the one closest to the input jack.